JPH03276906A - Oscillator circuit for pulse width transmission - Google Patents

Abstract

PURPOSE:To oscillate a clock with high accuracy and less frequency dispersion by adjusting a resistance for setting a time constant of a CR oscillator circuit with an analog switch and a nonvolatile memory. CONSTITUTION:A multiplex transmission circuit 3 is operated by a clock oscillated by a CR oscillator circuit 1 and applies time division multiplex transmission with a master set connecting to a transmission line Q. A resistance for setting time constant of the circuit 1 is varied freely by an analog switch SWi. The switch SWi is controlled to be ON or OFF state based on a data of an E<2>PROM2. Since data is written in the E<2>PROM2 in this way, the oscillating frequency of the circuit 1 is adjusted with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oscillation circuit for pulse width transmission, and is used, for example, in a terminal IC of a time division multiplex transmission system.

[Conventional technology] Conventionally, one base unit and multiple terminals are connected to a common transmission line, the base unit transmits time division multiplexed transmission signals, and each terminal is individually accessed and controlled. Time division multiplex transmission systems that provide data and return monitoring data are widely used. In such systems, pulse width transmission is often used in which long pulses correspond to 1'' and short pulses correspond to O''. In the terminal device, a clock is generated by a CR oscillation circuit, the clock is counted according to the received pulse width, and long pulses and short pulses are distinguished according to the count value. Although a large number of such terminals are used, it is preferable to use a single-chip IC.

[Problems to be Solved by the Invention] However, when a CR oscillation circuit is incorporated into a single chip IC, the oscillation frequency varies by 30% or more due to variations in the values of capacitors and resistors due to integration into the IC. For this reason, ICs with built-in oscillation circuits have not reached the level of practical use. Therefore, conventionally, it has been necessary to externally attach a clock oscillation circuit or its time constant circuit to the terminal IC.

The present invention has been made in view of these points, and its purpose is to suppress variations in oscillation frequency in an oscillation circuit for pulse width transmission. The purpose is to automatically adjust the oscillation frequency according to the received pulse width.

[Means for Solving the Problems] In order to solve the above problems, in the invention as claimed in claim 1, as shown in FIG. 1, a clock for determining the received pulse width of pulse width transmission is generated. A CR oscillation circuit 1 whose oscillation frequency is determined by the time constant of a capacitor and a resistor, an analog switch SWi for adjusting the value of the resistor, and a memory of the result of adjusting the value of the resistor by the analog switch SWi. non-volatile memory 2,
The device is characterized by comprising means for writing data into the nonvolatile memory 2.

In addition, in the invention as claimed in claim 2, as shown in FIG. The data setting circuit 12 further includes a data setting circuit 12 for setting data.

[Function] In the invention described in claim 1, since the value of the resistor for setting the time constant of the CR oscillation circuit 1 can be adjusted by the analog switch SWi and the nonvolatile memory 2, variations in circuit constants and power supply voltage can be avoided. Even if there is, from CR oscillation circuit 1,
It is possible to oscillate a highly accurate clock with little frequency variation.

In the invention according to claim 2, the counter 11 counts the clock according to the received pulse width, and the data setting circuit 12 sets the data in the nonvolatile memory 2 so that the counted value becomes a predetermined value. Because I made it to
It is possible to automatically oscillate a clock with a frequency suitable for determining the received pulse width.

[Embodiment] FIG. 1 is a block circuit diagram of an embodiment of the present invention. This circuit shows the internal configuration of a terminal IC for time division multiplex transmission, and includes a multiplex transmission circuit 3 that performs control for time division multiplex transmission, and a CR oscillation circuit 1 that provides an operating clock to this circuit. , an analog switch S W i for adjusting its oscillation frequency, and an E2PROM2.

The multiplex transmission circuit 3 is operated by the clock oscillated by the CR oscillation circuit 1, performs time-division multiplex transmission with the base unit connected to the transmission line Q, and transmits input data from the input/output port P to the base unit. The input/output boat P outputs a control signal under control from the base unit. The value of the resistor for setting the time constant of the CR oscillation circuit 1 can be freely changed using the analog switch S Wi . This analog switch SWi is controlled to be on or off based on data in the E2PROM2.

A specific circuit configuration for adjusting the value of the time constant setting resistor in the CR oscillation circuit 1 is shown in FIG. E2FR
Data D1 on the bus is sent to OM2 by write signal WR.
~D, is written. Analog switches SW+ to SWs are controlled to be on or off in correspondence to each bit of data D1 to D5 stored in the E2FROM2. Any analog switch 5Wi (i=
1 to 5) are in the on state, this switch SW
Since the resistor Ri corresponding to i is short-circuited, the resistance value between terminals A and B decreases by the short-circuited resistance. for example,
Data D, , D2 . stored in E2FROM2. D.I.

D = , D s is 0.0.1, 1. ．． If it is 1,
Switches SW+ and SW2 are turned off, and switch S
W,, SW4. The SWs are turned on. This results in
The resistance between terminals A and B is Ro + R+ + R2.

With the above method, the resistance between terminals A and B can be freely changed by the combination of R8 and R5 by writing data to E2PROM2/\. That is, the oscillation frequency of the CR oscillation circuit 1 can be adjusted.

By the way, as shown in FIG. 1, when the CR oscillation circuit 1 is built into a terminal IC, the oscillation frequency varies by 30% or more due to variations in circuit constants. Therefore, after manufacturing the IC, in order to adjust the oscillation frequency, take out the clock from the clock output terminal φ, measure the clock frequency, and set data to the data setting terminal Di of the E2PROM2 without checking the measurement result. This is to adjust the oscillation frequency to the rated value.

FIG. 2 is a block circuit diagram of another embodiment of the invention.

In this embodiment, the oscillation frequency of the clock is automatically adjusted according to the received pulse width. To this end, this embodiment includes a short pulse determination counter 11, a data setting circuit 12, and a short pulse detection circuit 13.

In a typical time division multiplex transmission system, the transmission signal
“,°゛0” is determined by the length of the pulse.

For example, assume that a short pulse means "0" and that the pulse length is 12571 seconds. Here, when the oscillation frequency of the clock is 100 kHz, the sampling interval of the received pulse is 10 μSee, so if the pulse length is 12 samplings, it is determined that the pulse is short. Therefore, on the terminal side, highly reliable transmission can be achieved by detecting the short pulse of the transmission signal sent from the base unit and adjusting the 5-clock oscillation frequency so that the pulse length has a sampling count of 12.

In order to realize the above, in this embodiment, the short pulse detection circuit 13 detects the short pulse of the multiplex transmission signal from the base unit, and detects the pulse change point. Based on this short pulse change point, the tarok from the CR oscillation circuit 1 is calculated by the counter 1.
Count by 1. The data setting circuit 12 determines whether the count counted by the counter 11 at the time of receiving the short pulse is 12 counts. And if the count number is 12 counts, E2PROM2
The data in E2PROM2 is left as is, and if the count number is not 12 counts, the data in the E2PROM2 is set so that the count number is 12 counts.

For example, as shown in FIGS. 4(a) and 4(b), if the number of clock counts between the changing points of the short pulse is 15, the data setting port v@12 is used to lower the oscillation frequency. Then, data is set in the E2PROM 2 for resistance adjustment, and a part of the analog switch S Wi is turned off. Thereby, the value of the resistance for setting the time constant of the CR oscillation circuit 1 can be increased. the result,
As shown in Figure 4(c), the short pulse count is 1.
A clock with an oscillation frequency that provides two counts can be obtained.

If the circuit of this example is used, even if the transmission signal waveform from the base unit is distorted due to the characteristics of the transmission path and the pulse width of the entire signal becomes longer, the terminal side will be able to detect the longer pulse width. Since a clock with a frequency suitable for pulse width detection is automatically generated, signal transmission can be performed normally. Furthermore, even if both the short pulse and long pulse width are set longer than the normal pulse width due to a change in the specifications of the base unit, the clock oscillation frequency will be automatically changed on the terminal side.
There is no need to replace the device.

Note that terminal ICs for time-division multiplex transmission often have a built-in E2PROM for setting the address of the own station, so a part of the storage area of this E2PROM can be used as a storage area for resistance value adjustment data. You may do so.

[Effects of the Invention] In the invention described in claim 1, as described above, since the value of the resistor for setting the time constant in the CR oscillation circuit can be adjusted by the analog switch and the nonvolatile memory, the nonvolatile memory The oscillation frequency of the CR oscillation circuit can be adjusted with high precision simply by writing data to the oscillation circuit, and even if there are variations in the power supply voltage and circuit constants, the variation in the oscillation frequency can be reduced. Therefore, there is an advantage that the entire device can be configured with one chip of IC.

In the invention according to claim 2, as described above, the clock is counted by a counter according to the received pulse width,
Since the data setting circuit writes data to non-volatile memory so that the count value becomes a predetermined value, even if the received pulse width changes due to changes in the specifications of the sender, fluctuations in the power supply, or characteristics of the transmission system, the Since a clock having a frequency suitable for receiving pulse widths is automatically oscillated, the reliability of pulse width transmission can be improved.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram of one embodiment of the present invention, Fig. 2 is a circuit diagram of the main parts of the same as above, Fig. 3 is a block circuit diagram of another embodiment of the present invention, and Fig. 4 is an explanation of the operation of the same as above. It is a diagram. 1 is a CR oscillation circuit, 2 is a nonvolatile memory, 3 is a multiplex transmission circuit, SWi is an analog switch, 11 is a short pulse determination counter, and 12 is a data setting circuit.

Claims (2)

[Claims] (1) In an oscillation circuit that generates a clock for determining the received pulse width of pulse width transmission, there is a CR oscillation circuit whose oscillation frequency is determined by the time constant of a capacitor and a resistor, and an analog switch for adjusting the value of the resistor. An oscillation circuit for pulse width transmission, comprising: a nonvolatile memory that stores the result of adjusting a resistance value by an analog switch; and means for writing data into the nonvolatile memory. (2) The device further comprises a counter that counts clocks according to the width of the received pulse, and a data setting circuit that sets data in the nonvolatile memory so that the count value of the counter becomes a predetermined value. Oscillation circuit for pulse width transmission described.