GB2595253A

GB2595253A - Device and method for detecting termination in communication unit in vehicle

Info

Publication number: GB2595253A
Application number: GB2007397.9A
Authority: GB
Inventors: Bharadwaj M V Pramod; Thangam Aiyam Pillai Balaji; Paul Luke Kingkam Durai Winnefred
Original assignee: Vitesco Technologies GmbH
Current assignee: Vitesco Technologies GmbH
Priority date: 2020-05-19
Filing date: 2020-05-19
Publication date: 2021-11-24
Also published as: GB202007397D0

Abstract

The termination resistance to which a communication unit in a vehicle is connected is determined by a differential amplifier Q12 connected to calculate a differential voltage between the bus lines 111, 112, and a comparator Q13 to compare the calculated differential voltage with a first predetermined value to detect that a termination resistor of the communication unit is open if the differential voltage is greater than or equal to the first predetermined value. If the differential voltage is less than the first predetermined value, a comparator Q14 is compares the differential voltage with a second predetermined value, to detect a resistance value of the termination resistor. The communication bus may be CAN bus or FlexRay. The comparators Q13, Q14 may be connected by an inverter N8, which may active the second comparator Q14 if the differential voltage is lower than the first threshold.

Description

DEVICE AND METHOD FOR DETECTING TERMINATION IN COMMUNICATION UNIT IN VEHICLE

TECHNICAL FIELD

The present invention relates to a device and method for detecting termination in a communication unit in a vehicle, and particularly relates to a device and method for detecting a resistance in which a termination resistor of the communication unit is connected to.

BACKGROUND

The following discussion of the background is intended to facilitate an understanding of the present invention only. It may be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge of the person skilled in the art in any jurisdiction as at the priority date of the present invention.

Typically, a communication bus, for example a Controller Area Network (hereinafter referred to as "CAN") bus, is a vehicle bus standard which allows devices such as micro-controllers to communicate with each other's applications without a host computer. CAN node includes a CAN communication transceiver which is operable to receive and transmit data. Specifically, the CAN communication transceiver may receive the data by converting the data stream from CAN bus levels to levels that a CAN controller uses. The CAN communication transceiver may transmit the data by converting the data stream from the CAN controller to the CAN bus levels.

However, the CAN communication transceiver which is used for the CAN data communication is prone to external disturbance such as improper termination. The damage of the CAN communication transceiver may hinder the CAN data communication. Hence, a diagnosis of the improper termination of the CAN communication transceiver may be required to ensure a stable CAN data communication.

In light of the above, there exists a need to provide a solution that meets the mentioned needs at least in part.

SUMMARY

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Furthermore, throughout the specification, unless the context requires otherwise, the word "include" or variations such as "includes" or "including", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

The present invention seeks to provide a device and a method that addresses the afore-mentioned need at least in part.

The technical solution is provided in the form of a device and a method for detecting a termination in a communication unit (for example, CAN communication transceiver (hereinafter referred to as "transceiver")) in a vehicle. The device may be installed or equipped in the communication unit. The device comprises a differential amplifier operable to calculate a differential voltage from voltages detected from differential communication lines (for example, CAN bus lines), and a comparator operable to compare the calculated differential voltage with a first predetermined value. If the calculated differential voltage is greater than or equal to the first predetermined value, the comparator is operable to detect that a termination resistor of the communication unit is open. If the calculated differential voltage is less than the first predetermined value, the comparator is further operable to compare the calculated differential voltage with a second predetermined value, so as to detect a resistance in which the termination resistor is connected to.

Therefore, the device in accordance with the present invention can detect the improper termination in the communication unit, since the comparator of the present invention can detect whether the termination resistor of the communication unit is open and detect the resistance in which the termination resistor is connected to. In this manner, the device can prevent the communication unit from the external disturbance, and thus ensure a stable data communication (for example, CAN data communication).

In accordance with an aspect of the present invention, there is a device for detecting a termination in a communication unit in a vehicle comprising: a differential amplifier operable to calculate a differential voltage from voltages detected from differential communication lines; and a comparator operable to compare the calculated differential voltage with a first predetermined value, and detect that a termination resistor of the communication unit is open if the calculated differential voltage is greater than or equal to the first predetermined value, characterised in that: if the calculated differential voltage is less than the first predetermined value, the comparator is further operable to compare the calculated differential voltage with a second predetermined value, so as to detect a resistance in which the termination resistor is connected to.

In some embodiments, the communication unit includes at least one of a transceiver and a transmitter.

In some embodiments, the differential communication lines include at least one of CAN bus lines and FlexRay bus lines.

In some embodiments, the CAN bus lines include a high level CAN bus line and a low level CAN bus line.

In some embodiments, the FlexRay bus lines include a bus plus line and a bus minus line.

In some embodiments, the differential amplifier is operable to calculate the differential 25 voltage from a voltage detected from the high level CAN bus line and a voltage detected from the low level CAN bus line.

In some embodiments, the comparator comprises a first comparator operable to compare the calculated differential voltage with the first predetermined value, and a second comparator operable to compare the calculated differential voltage with the second predetermined value.

In some embodiments, the second comparator is connected to the first comparator via an inverter.

In some embodiments, if the calculated differential voltage is less than the first predetermined value, the inverter is operable to activate the second comparator.

In some embodiments, if the calculated differential voltage is greater than or equal to the second predetermined value and is less than the first predetermined value, the second comparator is operable to detect that the resistance in which the termination resistor is connected to is 1200.

In some embodiments, if the calculated differential voltage is less than the second predetermined value, the second comparator and the inverter are operable to detect that the resistance in which the termination resistor is connected to is 60 D. In some embodiments, the device further comprises a CAN 16-bit status register, wherein the CAN 16-bit status register comprises a first bit connected to a first AND gate which is connected to the first comparator, a second bit connected to a second AND gate which is connected to the second comparator, and a third bit connected to a third AND gate which is connected to the second comparator via an inverter.

In some embodiments, if the calculated differential voltage is greater than or equal to the first predetermined value, the first comparator is operable to set the first bit to be a high level which indicates the CAN bus lines are open.

In some embodiments, if the calculated differential voltage is greater than or equal to the second predetermined value and is less than the first predetermined value, the second comparator is operable to set the second bit to be a high level which indicates 25 the CAN bus lines are connected to 120 0.

In some embodiments, if the calculated differential voltage is less than the second predetermined value, the second comparator and the inverter are operable to set the third bit to be a high level which indicates the CAN bus lines are connected to 60 0.

In some embodiments, the first predetermined value is 3V.

In some embodiments, the second predetermined value is 2.5V.

In accordance with another aspect of the present invention, there is a method for detecting a termination in a communication unit in a vehicle comprising steps of: calculating a differential voltage from voltages detected from differential communication lines; comparing the calculated differential voltage with a first predetermined value; if the calculated differential voltage is greater than or equal to the first predetermined value, detecting that a termination resistor of the communication unit is open; and if the calculated differential voltage is less than the first predetermined value, comparing the calculated differential voltage with a second predetermined value so as to detect a resistance in which the termination resistor is connected to.

In some embodiments, the method further comprises a step of: if the calculated differential voltage is greater than or equal to the second predetermined value and is less than the first predetermined value, detecting that the resistance in which the termination resistor is connected to is 120 D. In some embodiments, the method further comprises a step of: if the calculated differential voltage is less than the second predetermined value, detecting that the resistance in which the termination resistor is connected to is 60 0.

Other aspects of the invention will become apparent to those of ordinary skilled in the art upon review of the following description of specific embodiments of the present invention in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example only, with reference to 25 the accompanying drawings, in which: Figs. 1 and 2 are block diagrams showing a transceiver in accordance with an embodiment of the present invention.

Fig. 3 is a circuit diagram showing the transceiver in accordance with an embodiment of the present invention.

Fig. 4 is a circuit diagram for detecting a termination in a CAN communication transceiver in accordance with an embodiment of the present invention.

Fig. 5 is a circuit diagram for detecting SCB (short circuit to battery) and SCG (short circuit to ground) on CAN bus lines.

Fig. 6 is a circuit diagram for detecting a polarity reversal.

Fig. 7 is a circuit diagram for detecting power on and UV (undervoltage) of a voltage common collector.

Fig. 8 is a circuit diagram for detecting UV (undervoltage) of an input offset voltage.

Fig. 9 is a circuit diagram for detecting an open on a low level CAN bus line. Fig. 10 is a circuit diagram for detecting an open on a high level CAN bus line.

Fig. 11 is a circuit diagram for detecting a CAN switchable termination, where ENO (Enable 0) is "0" and EN1 (Enable 1) is "0".

Fig. 12 is a circuit diagram for detecting a CAN switchable termination, where ENO is "0" and EN1 is "1".

Fig. 13 is a circuit diagram for detecting a CAN switchable termination, where ENO is "1" and EN1 is "0".

Fig. 14 is a circuit diagram for detecting a CAN switchable termination, where ENO is "1" and EN1 is "1".

Fig. 15 is a flowchart in accordance with an embodiment of the present invention.

Other arrangements of the present invention are possible and, consequently, the accompanying drawings are not to be understood as superseding the generality of the preceding description of the invention.

DETAILED DESCRIPTION OF EMBODIMENT

Figs. 1 and 2 are block diagrams showing a transceiver in accordance with an embodiment of the present invention. Fig. 3 is a circuit diagram showing the transceiver in accordance with an embodiment of the present invention.

In accordance with the present invention, there is a communication unit. The communication unit may include, but not be limited to, a transceiver and a transmitter.

The transceiver may include a CAN (controller area network) IC (integrated circuit) transceiver (hereinafter referred to as "transceiver") 100, as shown in Fig. 1. The transceiver 100 may be an electronic device made of semiconductor material. Although not shown, the transceiver 100 may contain one or more microscopic elements including, but not limited to, transistors, capacitors and resistors.

The transceiver 100 may have a plurality of pins (for example, fourteen (14) pins). The pins can perform a predetermined function as shown in the below table 1.

Symbol Pin Description

TXD 1 Transmit data input GND 2 Ground VCC 3 Supply voltage 5V RXD 4 Receive data output VIO 5 Supply voltage 5V SDO 6 SPI data output NC 7 No connection SCK 8 SPI clock input SO 9 Switch 0 for switchable termination Si 10 Switch 1 for switchable termination SDI 11 SPI data input CANL 12 Low level CAN bus line CANH 13 High level CAN bus line SCSN 14 SPI chip select input [Table 1 CAN IC Transceiver] As shown in Figs. 2 and 3, the transceiver 100 may include, but not be limited to, a driver and control unit 102, a switchable termination 103, a serial peripheral interface (hereinafter referred to as "SPI") block 104 and a CAN diagnostics device 101 (also referred to as "CAN diagnostics unit").

The driver and control unit 102 is operable to communicate with differential communication lines. The differential communication lines may include, but not be limited to, CAN bus lines and FlexRay bus lines. The CAN bus lines include a high level CAN bus line and a low level CAN bus line. The FlexRay bus lines include a bus plus line and a bus minus line.

As shown in Fig. 2, the driver and control unit 102 is operable to receive the data by converting the data stream from CAN bus levels to levels that a CAN controller uses, and to transmit the data by converting the data stream from the CAN controller to the CAN bus levels.

The switchable termination 103 is operable to allow the CAN transceiver 100 to be selectively terminated via switches SO and Si.

The SPI block 104 is operable to control functions with a CAN 16-bit status register (as shown in the below table 2) to read on service data objects (hereinafter referred to as "SDO") indicating diagnostic functionalities.

Bits Description

BO High level indicates Power on B1 High level indicates UV_ Vcc B2 High level indicates UV_ Vio B3 High level indicates SCB on CANH B4 High level indicates SCG on CANH B5 High level indicates SCB on CANL B6 High level indicates SCG on CANL B7 High level indicates CAN lines without termination B8 High level indicates CAN lines with only 120ohm termination B9 High level indicates CAN lines with only 60ohm termination B10 High level indicates CANH open B11 High level indicates CANL open B12 High level indicates Polarity reversed on CAN Lines B13 High level indicates Over temperature B14 Reserved 1315 Parity status (XOR of status bits 0 to 14) [Table 2: CAN 16-bit Status Register] The CAN diagnostics device 101 is operable to perform a diagnosis feature such as a termination detection. The CAN diagnostics device 101 includes a device 101a (also referred to as "a unit") for detecting a termination in the transceiver 100. Specifically, the device 101a is operable to detect the termination in the transceiver 100, and a resistance in which a termination resistor of the transceiver 100 is connected to. The operation of the device 101a will be described below.

It may be appreciated that the CAN diagnostics device 101 is operable to perform additional diagnosis features such as power on detection, under voltage detection on voltage common collector (also referred to as "Vcc"), under voltage detection on input offset voltage (also referred to as "Vie"), short circuit to battery (hereinafter referred to as "SCB"), short circuit to ground (hereinafter referred to as "SCG"), open detection, and/or polarity reverse detection. It may be appreciated that the CAN diagnostics device 101 is further operable to support over temperature detection.

Fig. 4 is a circuit diagram for detecting a termination in a CAN communication transceiver in accordance with an embodiment of the present invention. Fig. 5 is a circuit diagram for detecting SCB and SCG on CAN bus lines. Fig. 6 is a circuit diagram for detecting polarity reversal.

As shown in Fig. 4, the device 101a may include a differential amplifier (012) and a comparator.

The differential amplifier (012) may be an electronic amplifier operable to calculate the difference between two input voltages. The differential amplifier (012) may be an analogue circuit with two inputs and one output.

Specifically, the differential amplifier (012) may calculate a differential voltage from two input voltages detected from CAN bus lines 111 and 112. More specifically, the differential amplifier (012) is connected to a high level CAN bus line (also referred to as "CANH") 111 and a low level CAN bus line (also referred to as "CANL") 112 respectively, and is operable to detect a voltage from the high level CAN bus line 111 and a voltage from the low level CAN bus line 112. Thereafter, the differential amplifier (012) is operable to calculate the differential voltage from the voltage detected from the high level CAN bus line 111 and the voltage detected from the low level CAN bus line 112.

In some embodiments, the differential amplifier (012) may amplify the calculated differential voltage. Therefore, the output of the differential amplifier (012) may be proportional to the difference between the two input voltages.

The comparator may be a device operable to compare two voltages or currents, and to output a digital signal indicating which voltage or current is larger. The comparator may have two analogue input terminals V+ and V_ (hereinafter referred to as "a first input terminal and a second input terminal") and one binary digital output Vo. For example, if the voltage of the first input terminal V+ is higher than the voltage of the second input terminal V as a predetermined value, the binary digital output Vo is 1. If however the voltage of the first input terminal V+ is less than the voltage of the second input terminal V_ as the predetermined value, the binary digital output Vo is 0.

In some embodiments, the comparator may include at least one comparator. For 15 example, as shown in Fig. 4, the comparator may include two comparators (013 and 014) (hereinafter referred to as "a first comparator (013) and a second comparator (Q14)").

The first comparator (013) may be connected to the differential amplifier (012) via the first input terminal V+. The first comparator (013) may receive the calculated differential voltage from the differential amplifier (012) via the first input terminal V+.

The first comparator (013) may be connected to one or more current sources (119 and 120) via the second input terminal V_. The current sources (119 and 120) are connected to a voltage common collector (hereinafter referred to as "Vcc"). Based on a current of the current sources (119 and 120) and a voltage of the Vcc, the voltage (hereinafter referred to as "first predetermined value") of the second input terminal V_ may be determined. For example, the first predetermined value is 3V.

In some embodiments, the predetermined value may be defined and set by a manufacturer. In some other embodiments, the predetermined value may be defined and set by a user. In some other embodiments, the predetermined value may be updated or changed. For example, a user may set an updated predetermined value by adjusting the current of the current sources (119 and 120) and the voltage of the Vcc.

If it is detected that the calculated differential voltage is greater than or equal to the first predetermined value by the first comparator (013), the first comparator (013) is operable to detect that a termination resistor of the transceiver is open.

In some embodiments, as shown in Fig. 4, an AND gate (hereinafter referred to as "first AND gate") (A5) is connected to the first comparator (013) and another AND gate (hereinafter referred to as "fourth AND gate") (A4). The fourth AND gate (A4) may be connected to a NOR gate (NR2) and a NOT gate (N6).

The NOR gate (NR2) may be connected to a circuit to detect a short circuit on CAN bus lines. As shown in Fig. 5, the NOR gate (NR2) can be connected to one or more comparators, for example four comparators (07, 08, 05 and 06). The comparators (07, Q8, 05 and Q6) are used to detect SCB on the high level CAN bus line, SCG on the high level CAN bus line, SCB on the low level CAN bus line and SCG on the low level CAN bus line respectively.

Specifically, SCB on the high level CAN bus line can be detected using the comparator (05) and fixed current sources (113 and 114). SCG on the high level CAN bus line can be detected using the comparator (06) and fixed current sources (111 and 112). SCB on the low level CAN bus line can be detected using the comparator (08) and fixed current sources (111 and 112). SCG on the low level CAN bus line can be detected using the comparator (07) and fixed current sources (113 and 114).

The status of the bits B3, B4, B5 and B6 (as shown in the below tables 3 and 4) can be read on the SDO line.

Condition B3 (CANH_SCB) B4 (CANH_SCG) 1 V<CANH<4V 0 0 CANH1 V 0 1 4V5CANH 1 0 [Table 3: SCB/SCG on CAN H] Condition B5 (CAN L_SCB) B6 (CANL_SCG) 1V<CANL<4V 0 0 CANIS V 0 1 4V5CANL 1 0 [Table 4: SCB/SCG on CANL] As shown in Fig. 4, the NOT gate (N6) is connected to a circuit to detect a polarity reversal. When the high level CAN bus line and the low level CAN bus line are interchanged, polarity reversal may occur. As shown in Fig. 6, the polarity reversal is detected using a comparator (09) and a NOT gate (N5). If there is SCB and/or SCG on CAN bus lines, polarity reversal is at low level (for example, "0"). The status of the bit B12 (as shown in the below table 5) can be read on the SDO line.

Condition B3 B4 B5 B6 B12

CANH_SCB CANH_SCG CANL_SCB CANL_SCG POL_REV

CANH<CANL 0 0 0 0 1 CANH<CANL 1 X X X 0 CANH<CANL X 1 X X 0 CANH<CANL X X 1 X 0 CANH<CANL X X X 1 0 CANH>CANL X X X X 0 [Table 5: Polarity reverse detection] It may be appreciated that if there is SCB and/or SCG or polarity reversal on CAN bus lines, the output may be low. In addition, the voltages may depend on the saturation currents of p-MOS and n-MOS during dominant phase.

It may be appreciated that a mathematical equation for differential voltage VD," is as follows: VDIFF = CANH -CANL The status of the bits B7, 38 and B9 (as shown in the below tables 6 and 7) can be read on the SDO line.

Condition B3 B4 B5 B6 B12 87 88 89 Open 1200 600 Connected Connected 3'/CANH-CANL 0 0 0 0 0 1 0 0 2.5WCANH-CANL<3V 0 0 0 0 0 0 1 0 CANH-CANL<2.5V 0 0 0 0 0 0 0 1 X 1 X X X X 0 0 0 X X 1 X X X 0 0 0 X x x 1 x x 0 0 0 X X X X 1 X 0 0 0 X x x x x 1 0 0 0 [Table 6: Terminal detection] End Node 1 End Node 2 Output Open Open B7 = 1 (Open) 1200 Open B8 = 1 (1200 Connected) Open 1200 B8 = 1 (1200 Connected) 1200 1200 B9 = 1(600 Connected) [Table 7: Terminal detection] As shown in Fig. 4, the first AND gate (A5) is connected to the first comparator (Q13) and the fourth AND gate (A4). The fourth AND gate (A4) may be connected to a NOR gate (NR2) and a NOT gate (N6). In this regard, where SCB and SCG are not detected on the CAN bus lines and the polarity reversal is not detected, both the NOR gate (NR2) and the NOT gate (N6) may output "1". Thus, the fourth AND gate (A4) may output "1", and then the first AND gate (A5) may output "1" if the calculated differential voltage is greater than or equal to the first predetermined value (for example, 3V).

Therefore, the device 101a can detect that the termination resistor of the transceiver is open, based on the output of the first AND gate (A5).

If however, the calculated differential voltage is less than the first predetermined value (for example, 3V), a second comparator (Q14) may be used. The second comparator (014) is connected to the first comparator (013) via a NOT gate (N8) (also referred to as "inverter"). In some embodiments, if the calculated differential voltage is less than the first predetermined value, the NOT gate (N8) is operable to activate the second comparator (014).

The second comparator (014) may be connected to the differential amplifier (012) via the first input terminal V+. The second comparator (014) may receive the calculated differential voltage from the differential amplifier (012) via the first input terminal V+.

The second comparator (014) may be connected to one or more current sources (121 and 122) via the second input terminal The current sources (121 and 122) are connected to a voltage common collector (hereinafter referred to as "Vcc"). Based on a current of the current sources (121 and 122) and a voltage of the Vcc, the voltage (hereinafter referred to as "second predetermined value") of the second input terminal V_ may be determined. It may be appreciated that the second predetermined value is less than the first predetermined value. For example, the second predetermined value is 2.5V.

If it is detected that the calculated differential voltage is less than the first predetermined value (for example, 3V) by the first comparator (013) and is greater than or equal to the second predetermined value (for example, 2.5V) by the second comparator (014), the second comparator (014) is operable to detect that the resistance in which the termination resistor is connected to is 120 0.

More specifically, as shown in Fig. 4, an AND gate (A6) (hereinafter referred to as "second AND gate") is connected to the second comparator (014) and the fourth AND gate (A4). The fourth AND gate (A4) may be connected to the NOR gate (N R2) and the NOT gate (N6). In this regard, where SCB and SCG are not detected on the CAN bus lines and the polarity reversal is not detected, both the NOR gate (N R2) and the NOT gate (N6) may output "1". Thus, the fourth AND gate (A4) may output "1", and then the second AND gate (A6) may output "1" if the calculated differential voltage is less than the first predetermined value (for example, 3V) and is greater than or equal to the second predetermined value (for example, 2.5V). Therefore, the device 101a can detect that the termination resistor of the transceiver 100 is connected to 120 0, based on the output of the second AND gate (A6).

If however it is detected that the calculated differential voltage is less than the second predetermined value (for example, 2.5V) by the second comparator (014), the second comparator (014) is operable to detect that the resistance in which the termination resistor is connected to is 60 0.

More specifically, as shown in Fig. 4, an AND gate (A7) (hereinafter referred to as "third AND gate") is connected to the second comparator (014) via a NOT gate (N7) (also referred to as "inverter"), and the fourth AND gate (A4). The fourth AND gate (A4) may be connected to the NOR gate (NR2) and the NOT gate (N6). In this regard, where SCB and SCG are not detected on the CAN bus lines and the polarity reversal is not detected, both the NOR gate (NR2) and the NOT gate (N6) may output "1". Thus, the fourth AND gate (A4) may output "1", and then the third AND gate (A7) may output "1" if the calculated differential voltage is less than the second predetermined value (for example, 2.5V). Therefore, the device 101a can detect that the termination resistor of the transceiver 100 is connected to 60 0, based on the output of the third AND gate (A7).

As described in the above table 2, the CAN 16-bit status register comprises a plurality of bits. The CAN 16-bit status register comprises B7 (hereinafter referred to as "first bit") connected to the first AND gate (A5), B8 (hereinafter referred to as "second bit") connected to the second AND gate (A6), and B9 (hereinafter referred to as "third bit") connected to the third AND gate (A7).

If the calculated differential voltage is greater than or equal to the first predetermined value, the first comparator (013) is operable to set the first bit to be a high level which indicates CAN bus lines are open. If the calculated differential voltage is greater than or equal to the second predetermined value and is less than the first predetermined value, the second comparator (014) is operable to set the second bit to be a high level which indicates CAN bus lines are connected to 120 0. If the calculated differential voltage is less than the second predetermined value, the second comparator (014) and the NOT gate (N7) are operable to set the third bit to be a high level which indicates CAN bus lines are connected to 60 D. In this manner, the present invention can prevent the transceiver 100 from the external disturbance by detecting the improper termination in the transceiver 100, and thus 30 ensure a stable CAN data communication.

In addition to the afore-mentioned features, the CAN IC transceiver 100 may perform further diagnosis to be described below.

Fig. 7 is a circuit diagram for detecting power on and UV (undervoltage) of a voltage common collector (Vcc).

"Power on" is detected at 3V using a comparator (03) and fixed current sources (14 and 15). The status of the bit BO (as shown in the above table 2) can be read on the SDO line.

The undervoltage of Vcc is detected at 3V using a comparator (02) and fixed current sources (16 and 17). The status of the bit B1 (as shown in the below table 8) can be 10 read on the SDO line. Pulsed voltage source is provided at Vcc switching from 0 to 5V at 500Hz.

Condition BO (Power on detection) B1 (Vcc Under voltage detection) Vcc 3V 0 1 Vcc > 3V 1 0 [Table 8: Power on and Vcc_UV detection] Fig. 8 is a circuit diagram for detecting UV (undervoltage) of an input offset voltage (Via).

The undervoltage of Via is detected at 3V using a comparator (04) and fixed current sources (18 and 19). Pulsed voltage source is provided at Via switching from 0 to 5V at 500Hz.The status of the bit B2 of the CAN 16-bit status register (as shown in the below table 9) can be read on the SDO line.

Condition B2 (V10 Under voltage detection) VIO 3V 1 VIO > 3V 0 [Table 9: Via_UV detection] Fig. 9 is a circuit diagram for detecting an open on a low level CAN bus line, and Fig. is a circuit diagram for detecting an open on a high level CAN bus line.

The open on the low level CAN bus line is detected if the low level CAN bus line goes beyond 3V provided there is no SCB/SCG on the CAN bus lines. For such detection, a comparator (011) and current sources (115 and 116) are used. The status of the bit B11 (as shown in the below table 10) can be read on the SDO line.

The open on the high level CAN bus line is detected if the high level CAN bus line goes less than 2V provided there is no SCB/SCG on the CAN bus lines. For such detection, a comparator (010) and current sources (117 and 118) are used. The status of the bit B10 (as shown in the below table 10) can be read on the SDO line.

Condition B3 B4 B5 B6 B10 B11

CANH_ CANH_ CANL_ CANL_ CANH_ CANL_

SCB SCG SCB SCG Open Open CANH>2V, CANL<3V 0 0 0 0 0 0 CANH>2V, CANL>3V 0 0 0 0 0 1 CANH<2V, CANLCV 0 0 0 0 1 0 X 1 X X X 0 0 X X 1 X X 0 0 X X X 1 X 0 0 X X X X 1 0 0 [Table 10: Open detection] Figs. 11 to 14 are circuit diagrams for detecting a CAN switchable termination.

Switchable termination option is provided for the CAN bus lines as shown in the below table 11. Such detection can be done by the external select pins SO and 51 or via SPI (serial peripheral interface) to finally generate ENO and EN1. This method may save PCB (printed circuit board) area and cost.

SO Si Termination Resistance 0 X 33k0 (Intermediate node) 1 0 1200 (End node) 1 1 600 (Intermediate node without end nodes termination) [Table 11: Switchable Termination] In the circuit diagrams, ENO and EN1 are generated by the external select pins SO and Si. The four different cases are to be discussed below. This termination network is connected in parallel to the CAN bus lines. An external termination can also be connected if the cases are "00" or "01".

Fig 11 is a circuit diagram for detecting a CAN switchable termination, where ENO is "0" and EN1 is "0".

When ENO is "0" and EN1 is "0", a resistor (R6) is 33k0 (33 kfl may be considered as an example for high ohmic). The resistor (R6) may act as a termination resistor for the CAN bus lines. This termination network may be used at intermediate nodes with end nodes terminated at 1200. During a dominant phase, the current flow may be 60.74uA.

When ENO is "0" and EN1 is "1", the resistor (R6) is 33k0 (33 kf2 may be considered as an example for high ohmic). The resistor (R6) may act as the termination resistor for the CAN bus lines. This termination network may be used at intermediate nodes with end nodes terminated at 120f1. During the dominant phase, the current flow may be 60.74uA. The current flow where ENO is "0" and EN1 is "1" may be the same as the current flow where ENO is "0" and EN1 is "0".

When ENO is "1" and EN1 is "0", the resistor (R6) is in parallel with the sum of "R4 and R5" (i.e. 600x2+4.7nF). Therefore, the resistor (R6) may act as the termination network for the CAN bus lines. During the dominant phase, the current flow may be 16.7mA. This termination network can be used at the end nodes.

When ENO is "1" and EN1 is "1", the resistor R6 is in parallel with the sum of "R4 and R5" and R3. Therefore, the resistor R6 may act as the termination network for the CAN bus lines. During the dominant phase, the current flow may be 33.39mA. This termination network can be used to at an intermediate node without end nodes terminated.

As shown in Fig. 4, the differential amplifier calculates a differential voltage from voltages detected from differential communication lines, for example CAN bus lines (S110). The comparator then compares the calculated differential voltage with a first predetermined value (3120).

Where the calculated differential voltage is greater than or equal to the first predetermined value (3130), the comparator detects that a termination resistor of a communication unit, for example a transceiver, is open (3140).

However, where the calculated differential voltage is less than the first predetermined value (3130), the comparator compares the calculated differential voltage with a second predetermined value (S150). Thereafter, the comparator is able to detect a resistance in which the termination resistor is connected to (5160).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims. However, this is merely an exemplarily embodiment, and those skilled in the art will recognize that various modifications and equivalents are possible in light of the above embodiments.

LIST OF REFERENCE SIGNS

100: Transceiver 101: CAN diagnostics device 101a: Device for detecting termination 102: Driver and control unit 103: Switchable termination 104: SPI block 111: High level CAN bus line (CANN) 112: Low level CAN bus line (CANL)

Claims

CLAIMS1. A device for detecting a termination in a communication unit in a vehicle comprising: a differential amplifier operable to calculate a differential voltage from voltages detected from differential communication lines; and a comparator operable to compare the calculated differential voltage with a first predetermined value, and detect that a termination resistor of the communication unit is open if the calculated differential voltage is greater than or equal to the first predetermined value, characterised in that: if the calculated differential voltage is less than the first predetermined value, the comparator is further operable to compare the calculated differential voltage with a second predetermined value, so as to detect a resistance in which the termination resistor is connected to.
2. The device according to claim 1, wherein the communication unit includes at least one of a transceiver and a transmitter.
3. The device according to claim 2, wherein the differential communication lines include at least one of CAN bus lines and FlexRay bus lines.
4. The device according to claim 3, wherein the CAN bus lines include a high level CAN bus line and a low level CAN bus line.
5. The device according to claim 3, wherein the FlexRay bus lines include a bus plus line and a bus minus line.
6. The device according to claim 4, wherein the differential amplifier is operable to calculate the differential voltage from a voltage detected from the high level CAN bus line and a voltage detected from the low level CAN bus line.
7. The device according to claim 4, wherein the comparator comprises a first comparator operable to compare the calculated differential voltage with the first predetermined value, and a second comparator operable to compare the calculated differential voltage with the second predetermined value.
8. The device according to claim 7, wherein the second comparator is connected to the first comparator via an inverter.
9. The device according to claim 8, wherein if the calculated differential voltage is less than the first predetermined value, the inverter is operable to activate the second comparator.
10. The device according to claim 9, wherein if the calculated differential voltage is greater than or equal to the second predetermined value and is less than the first 20 predetermined value, the second comparator is operable to detect that the resistance in which the termination resistor is connected to is 120 0.
11. The device according to claim 9, wherein if the calculated differential voltage is less than the second predetermined value, the second comparator and the inverter are operable to detect that the resistance in which the termination resistor is connected to is 60 O.
12. The device according to claim 9 further comprising a CAN 16-bit status register, wherein the CAN 16-bit status register comprises a first bit connected to a first AND gate which is connected to the first comparator, a second bit connected to a second AND gate which is connected to the second comparator, and a third bit connected to a third AND gate which is connected to the second comparator via an inverter.
13. The device according to claim 12, wherein if the calculated differential voltage is greater than or equal to the first predetermined value, the first comparator is operable to set the first bit to be a high level which indicates the CAN bus lines are open.
14. The device according to claim 12, wherein if the calculated differential voltage is greater than or equal to the second predetermined value and is less than the first predetermined value, the second comparator is operable to set the second bit to be a high level which indicates the CAN bus lines are connected to 1200.
15. The device according to claim 12, wherein if the calculated differential voltage is less than the second predetermined value, the second comparator and the inverter are operable to set the third bit to be a high level which indicates the CAN bus lines are 20 connected to 60 0.
16. The device according to claim 1, wherein the first predetermined value is 3V.
17. The device according to claim 1, wherein the second predetermined value is 25 2.5V.
18. A method for detecting a termination in a communication unit in a vehicle comprising steps of: calculating a differential voltage from voltages detected from differential communication lines; comparing the calculated differential voltage with a first predetermined value; if the calculated differential voltage is greater than or equal to the first predetermined value, detecting that a termination resistor of the communication unit is open; and if the calculated differential voltage is less than the first predetermined value, comparing the calculated differential voltage with a second predetermined value so as to detect a resistance in which the termination resistor is connected to.
19. The method according to claim 18 further comprising a step of: if the calculated differential voltage is greater than or equal to the second predetermined value and is less than the first predetermined value, detecting that the resistance in which the termination resistor is connected to is 120 0.
20. The method according to claim 18 further comprising a step of: if the calculated differential voltage is less than the second predetermined value, detecting that the resistance in which the termination resistor is connected to is 60 0.