JPH05108224A - Terminating resistor circuit - Google Patents

Abstract

PURPOSE:To provide a terminating resistor circuit capable of stably transmitting a signal between SCSI devices even when a source voltage is fluctuated by an external noise without consuming excessive power wastefully in a state where a bus is set freely. CONSTITUTION:The input terminal 5a of a regulator 5 is connected to a power source line 4a, and the output terminal 5b of the regulator 5 to a terminal 6a of a first terminating resistor 6 and a terminal 7b of a second terminating resistor 7. Also, the ground terminal 5c of the regulator 5 is connected to the ground line 4d, and the other terminal 6b of the first terminating resistor 6 is connected to a first signal line 4b, and the other terminal 7b of the second terminating resistor 7 to a second signal line 4b. Furthermore, the other terminal 6b of the first terminating resistor 6 is connected to the other terminal 7b of the second terminating resistor 7 by using a third terminating resistor 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to SCSI (Small).
Computer System Interfac
e) Termination resistance circuit in a system, and more particularly, to termination resistance circuit between computer devices in a differential type SCSI system.

[0002]

2. Description of the Related Art First, an interface of computer equipment will be briefly described. Conventionally, GP for automatic measurement has been used as a standard interface for small computers.
-IB, RS-232C for communication, etc. are known.
These are used by being incorporated in the host computer or optionally added to the board. The electrical specifications and execution procedures of each interface are determined by the required function, and the connection with the host is configured so that the electrical levels are the same on the bus lines described below.

The interface of the SCSI specification is similar to the connection with the host, and the SCSI interface is used to connect to the host.
It is used to access the system bus line. SC
In the SI system, a device that sends a command, such as a host computer, is called an initiator, and a device that executes a command, such as a hard disk or a printer, is called a target. However, in a SCSI system, in some cases, the initiator can be the target, and conversely, the target can be the initiator. The initiator and target are connected by a bus line called a SCSI bus. The devices existing on this SCSI bus are called SCSI devices without distinguishing between initiators and targets, but up to eight SCSI devices can be connected on the SCSI bus.

The signals on the SCSI bus are, for example, in the case of the single end type, and are configured as shown in FIG. In this figure, 21 is an initiator and 22 is a target. As shown in this figure, the SCSI bus is composed of a total of 18 signal lines including the upper 9 data signals (including one odd parity bit) and the lower 9 control signals. These are all handled with 0 and 1 signals. The differential type described in the present embodiment is provided with another 18 signal lines for transmitting a signal that is inverted from the signal on the 18 signal lines. By providing another signal line for transmitting a signal to be inverted in this way, noise can be canceled by two signal lines even if the signal line contains noise, and the signal can be transmitted stably. You can do it.

FIG. 4 shows an example of connection between the differential type initiator 21 and the target 22. As shown in this figure, the initiator 21 and the target 22 are connected by a bus line 23. In this figure, 2
4a is a power supply line to which + 5V is normally applied. 24b
Is a first signal line, and although only one line is shown, it is actually composed of 18 lines. Two
Reference numeral 4c is a second signal line for transmitting a signal which is the inverse of the signal on the first signal line 24b, and although only one line is shown in the figure, there are actually 18 lines. 24d is an earth line, and there are actually a plurality of lines. 24e is a driver and 24f is a receiver, and the signals of the two signal lines 24b and 24c are inverted by the driver 24e and the receiver 24f. 24g is driver 24e, receiver 24
This is a control end for inputting a signal for driving f. Power supply line 24a, signal lines 24b, 24c,
The earth line 24d is collectively referred to as a bus line.

Reference numeral 25 is a terminating resistor (terminator),
The first terminating resistor 26, the third terminating resistor 28, and the second terminating resistor 27, which are three terminating resistors connected in series, are connected between the power line 24a and the ground line 24d,
The connection point between the terminating resistor 26 and the third terminating resistor 28 of the first
The connection point between the second terminating resistor 27 and the third terminating resistor 28 is connected to the second signal line 24c. This terminating resistor 25 is SCS
Since it is necessary to match the impedance with the bus line cable in order to transmit the 0 and 1 signals between the I devices as an accurate rectangular wave, it is necessary to connect them to the SCSI devices at both ends. In the SCSI system, this terminating resistor 25 needs to be provided for each signal line for each device at both ends, and its resistance value is 330 in the case of the circuit of FIG.
Ω and 27 are defined as 150Ω. In such a terminating resistor circuit, the impedance of the terminating resistor 25 seen from the first signal line 24b and the second signal line 24c is about 196Ω. The determination of the 0 and 1 signals is made by comparing the voltage level of the first signal line 4b and the voltage level of the second signal line 4c.

[0007]

However, in the above-mentioned conventional termination resistance circuit, since the power supply line 24a is connected to the signal lines 24b and 24c through the termination resistance 25, noise is introduced into the power supply line 24a. If this happens, the voltage supplied from the power supply line 24a to the signal lines 24b and 24c will fluctuate. As a result, it becomes impossible to accurately compare and determine the signal levels of the signal lines 24b and 24c, and 0, 1 between the SCSI devices can be determined.
There is a disadvantage that it becomes difficult to stably transmit a signal as an accurate rectangular wave. Further, in the conventional termination resistance circuit, the power supply line 24a is connected to the earth line 24d through the termination resistance 25, so that no signal is transmitted on the signal lines 24b and 24c, that is, when the bus is free. However, since a current flows through the terminating resistor 25, there is a disadvantage that extra power is consumed.

The present invention has been made in view of the above problems, and can stably transmit a signal between SCSI devices even when the power supply voltage fluctuates due to external noise, and at the time of bus free. It is an object of the present invention to provide a terminating resistance circuit that does not consume extra power.

[0009]

In order to achieve the above object, the termination resistance circuit of the present invention connects the input end of the regulator to the power supply line and connects the output end of the regulator to one end of the first termination resistor. 2 is connected to one end of the terminating resistor, the ground end of the regulator is connected to the earth line, the other end of the first terminating resistor is connected to the first signal line, and the other end of the second terminating resistor is connected to the first The second terminating resistor is connected to the second signal line, and the other end of the first terminating resistor and the other end of the second terminating resistor are connected to each other by the third terminating resistor.

[0010]

Since the terminating resistor circuit of the present invention is configured as described above, it is possible to supply a stable voltage to the signal line side by the regulator. Signals between devices can be stably transmitted. Further, since the regulator is not connected to the ground line via the terminating resistor, extra power is not consumed when the bus is free.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. First, FIG. 1 is a diagram for explaining a termination resistance circuit according to an embodiment of the present invention.
It is an example of connection of computer equipment in a SCSI system of YPE. In this figure, 1 is an initiator, 2 is
Is a target such as a CD-ROM device, and 3 is a SCSI bus line that connects the initiator 1 and the target 2. For the bus line 3, a cable with a connector having 50 terminals or 68 terminals is used. This bus line 3
It includes a power supply line 4a, a first signal line 4b, a second signal line 4c, and a ground line 4d. The power supply line 4a is composed of one line, and its voltage is usually + 5V. 4b is the first signal line shown in FIG. 3, and although only one line is shown, it is actually 1
It consists of 8 lines. Reference numeral 4c is a second signal line for transmitting a signal which is the inverse of the signal of the first signal line shown in FIG. 3, and although this also shows only one line, there are actually 18 lines. .. The signals on the first signal line 4b and the second signal line 4c are such that when the signal on the first signal line 4b is at a high level, the signal on the second signal line 4c is at a low level, When the signal of 4b is low level, the signals of the second signal line 4c are inverted to each other so as to be high level. For example, the signal of the first signal line 4b is high level and the signal of the second signal line 4c is high. Is 1 when the signal is low level, and 0 when the signal on the first signal line 4b is low level and the signal on the second signal line 4c is high level. The inversion of the signals on the signal lines 4b and 4c is performed by the driver 4e and the receiver 4f. 4g is a driver 4
e, a control end for inputting a signal for driving the receiver 4f.

Reference numeral 5 indicates, for example, an input end 5a and an output end 5b.
And a ground terminal 5c, the input terminal 5a is connected to the power supply line 4a, the output terminal 5b is connected to one end 6a and 7a of two terminating resistors (terminators) 6 and 7, which will be described later, and the ground terminal. 5c is connected to the earth line 4d. The regulator 5 serves to make the power supply voltage from the power supply line 4a constant, for example, 2.5 V, and to supply the constant voltage to the signal lines 4b and 4c side. 6 is a first terminating resistor whose one end 6a is connected to the output end 5b of the regulator 5 and the other end 6b is connected to the first signal line 4b, and 7 is one end 7a of which is the output of the regulator 5. Edge 5b
Is a second terminating resistor connected to the second signal line 4c at the other end 7b, and the resistance values of the first terminating resistor 6 and the second terminating resistor 7 are, for example,
It is 330Ω. Reference numeral 8 is a third terminating resistor connected to the other end 6b of the first terminating resistor 6 and the other end 7b of the second terminating resistor 7, and its resistance value is, for example, 150Ω.

The terminating resistor 9 composed of such terminating resistors 6, 7 and 8 is used to transmit 0 and 1 signals between SCSI devices such as the initiator 1 and the target 2 as an accurate rectangular wave between lines. In order to match the impedance in the above, and it is necessary to provide the SCSI devices such as the initiator 1 and the target 2 at both ends respectively. In such a terminating resistor circuit, the impedance of the terminating resistor 9 viewed from the first signal line 4b is a combined resistance of the first terminating resistor 6, the second terminating resistor 7 and the third terminating resistor 8. , Is connected in parallel, the terminating resistors 6 and 7 are 330Ω, and the terminating resistor 8 is 150Ω, the value is about 196Ω. Similarly, the impedance of the terminating resistor 9 viewed from the second signal line 4c is the same as that of the second terminating resistor 7.
A combined resistance of the first terminating resistor 6 and the third terminating resistor 8;
Is approximately 196 because it is equal to
It becomes Ω. Therefore, the impedances of the terminating resistors 9 as viewed from the signal lines 4b and 4c are both about 196Ω, which can be set to a value equivalent to that of the conventional circuit of FIG.
In addition, this terminating resistor 6 is a differential type.
In the case of the circuit of, the signal lines 4b and 4 for each device
It is necessary to provide as many as c, that is, 18 sets.
Reference numeral 10 denotes an input end 5a and an output end 5b of the regulator 5.
Is a capacitor provided between the power supply line 4a and the output end 5b side of the regulator 5, and is a capacitor provided between the power supply line 4a and the ground line 4d.

FIG. 2 is a diagram showing a main part of the termination resistance circuit of the present invention. Points A, B, C, and D in this figure are:
It corresponds to points A, B, C, and D in FIG. If the parts shown in FIG. 2 are integrated by hybrid IC technology or the like, assembly of devices such as SCSI devices becomes easy.

In the terminating resistance circuit of the present invention configured as described above, the regulator 5 is not limited to the one having three terminals as in the embodiment, and the capacitor 7 is not always necessary. is not.

[0016]

Since the termination resistance circuit of the present invention is configured as described above, it is possible to stably transmit a signal between SCSI devices even if the power supply voltage fluctuates due to external noise, and This has the effect of not consuming extra power when the bus is free.

[Brief description of drawings]

FIG. 1 is an internal connection diagram for explaining a connection example of a computer device to which the present invention is applied.

FIG. 2 is a diagram showing a main part of the present invention.

FIG. 3 is a schematic diagram of signals on a SCSI bus.

FIG. 4 is an internal connection diagram for explaining a connection example of a conventional computer device.

[Explanation of symbols]

 1 Target 2 Initiator 3 Bus Line 4a Power Line 4b First Signal Line 4c Second Signal Line 4d Earth Line 4e Driver 4f Receiver 4g Control Terminal 5 Regulator 5a Input Terminal 5b Output Terminal 5c Ground Terminal 6 First Termination Resistor 6a One end 6b Other end 7 Second terminating resistor 7a One end 7b Other end 8 Third terminating resistor 9 Terminating resistor 10 Capacitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor William Kutsch 2 26-10 Tenjin Tenjin, Nagaokakyo City, Kyoto Prefecture Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] 1. A power supply line (4a) and a first signal line (4) connected between computer equipment (1) and (2).
b), a second signal line (4c) for transmitting a signal that is the inverse of the signal of the first signal line (4b), and the ground line (4d) are respectively connected via resistors.
It is a termination resistance circuit, and the power line (4a) is connected to the input terminal (5) of the regulator (5).
a), the output end (5b) of the regulator (5) is connected to one end (6a) of the first terminating resistor (6) and one end (7b) of the second terminating resistor (7), (5)
Connect the ground end (5c) of the to the ground line (4d),
The other end (6b) of the first terminating resistor (6) is connected to the first signal line (4b), and the other end (7) of the second terminating resistor (7) is connected.
b) is connected to the second signal line (4c), and the other end (6b) of the first terminating resistor (6) and the other end (7b) of the second terminating resistor (7) are connected to the third end. A terminating resistor circuit characterized by being connected with the terminating resistor (8).