JPH07147581A - Changeover device for input/output module - Google Patents

Abstract

PURPOSE:To conduct a control operation or the like between plural input output modules without increasing a load to a bus driver by controlling application of a power supply voltage depending on the information as to whether or not access to the input/output module accesses a back plane bus. CONSTITUTION:When a PIO (process input/output module) is not in use, a CPU sends a '0' level control signal to a terminal D of a register RG. A level of a Q terminal output of the register RG is logical L, a transistor TR 2 is turned off and then a TR 1 is turned off. Thus, a power supply side terminal of the PIO is made open and no power supply voltage Vcc is applied to a pull-up resistor Rp. On the other hand, when the PIO is in use, a level, '1' signal is sent from the CPU to the terminal D of the RG. The Q terminal of the register RG is logical H, the TR 2 is conductive and then the TR 1 is also conductive. Thus, the power supply side terminal is connected to the power supply and the power supply voltage Vcc is applied to the resistor Rp and an OCD is activated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching device used when a plurality of input / output modules including open collector output type drivers and pull-up resistors are connected to the same bus.

[0002]

2. Description of the Related Art In a control device such as a process controller, it is common to connect a plurality of process input / output modules (PIO) on one backplane. In such a configuration, as shown in FIG. 2, in order to exchange information between a plurality of PIO ₁ to PIO _n on the same backplane, or one PIO controls another PIO, In some cases, a bus B is provided on the backplane so that each PIO can access another PIO via this bus B.

[0003]

By the way, as a basic function of a PIO, when a PIO is inserted into or removed from a backplane, it is required that other PIO on the backplane should not be affected. In order to satisfy this requirement, an open collector output type driver (hereinafter referred to as "OCD") is often used as the driver 1 connected to the backplane bus B in each PIO of FIG. The reason is that when the OCD is used, a high impedance state can be maintained when connecting and disconnecting with respect to the backplane bus B, so that current does not flow into other PIO and excessive voltage is not applied. Because.

When this OCD is used, a pull-up resistor is indispensable, but if the resistance value is large, the rise of the signal will be gentle, so the size of the resistance value is limited.

A PIO having such a pull-up resistor R
When n are connected, the pull-up resistance seen from the bus driver (not shown) becomes R / n, so the load increases n times, and as a result, the capacity of the bus driver may be exceeded. For example, if R = 1 kΩ and n = 12, then V _CC / (R / n) = 5 V / (1 k / 12) = 60 mA, and the drive capability of an IC such as TTL is 4
Since it is 0 mA, normal operation cannot be performed.

Therefore, in the above example, 12 PIOs are used.
If a limit that only 6 of them can access the backplane bus B is set, the load of 30 mA should be sufficient. However, the other six units still remain as loads electrically, so that the load will end up being 60 mA.

Therefore, an object of the present invention is to connect a plurality of input / output modules including OCD to the same bus.
A pull-up resistor of an input / output module that does not access the backplane bus controls a power supply so as not to load the bus driver, thereby providing a switching device that reduces the load on the bus driver.

[0008]

SUMMARY OF THE INVENTION The present invention is a switching device used when connecting a plurality of input / output modules including an open collector output type driver and pull-up resistors to the same bus. Are configured to switch power supply to the power supply side terminal of the pull-up resistor of the input / output module depending on whether or not to access another input / output module via the bus.

[0009]

According to the present invention, the supply of the power supply voltage is controlled by the information as to whether the input / output module accesses the backplane bus. That is, the power supply side terminal of the pull-up resistor of the I / O module that does not access the backplane bus is opened without supplying the power supply voltage, while the power supply side terminal of the pull-up resistor of the I / O module that accesses the backplane bus is opened. Supply the power supply voltage.

As a result, even if there are many input / output modules to be connected to the backplane bus, a plurality of input / output modules can be supported on the same backplane without increasing the load on the bus driver.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit configuration of an embodiment in which the present invention is applied to a PIO including an open collector output type driver (OCD).

The PIO shown in the figure includes a transistor forming an OCD, and a pull-up resistor R _P having one end connected to its collector terminal and the other end connected to an external power supply V _CC (for example, 5 V). When a digital signal is input to the base terminal of the transistor, its "H",
When the transistor is turned on and off according to "L", an output signal from the collector terminal to the backplane bus is generated. Such PIO is the same as the conventional one.

According to the present invention, the above PIO is provided with a switching device for switching the power supply to the power supply side terminal of the pull-up resistor R _P. This switching device includes a first transistor Tr1 provided between a power source and a power source side terminal of a pull-up resistor R _P , a first resistor R1 having one end connected to its base terminal, and another resistor R1. A second transistor Tr2 provided between the end and the ground, a second resistor R2 having one end connected to its base terminal, and this resistor R2.
2 and the register RG connected to the other end.

The register RG turns on and off the second transistor Tr2 in response to a control signal sent from a control device such as a process or a CPU of a PIO host device. As such a register RG, a DQ flip-flop is used, for example. In this case, the D terminal of the DQ flip-flop is connected to the CPU, while the Q terminal is connected to the base terminal of the second transistor Tr2 via the resistor R2. Further, the signal latched at the rising edge is input from the CPU to the CK (clock) terminal of the DQ flip-flop.

The control signal is, for example, a digital signal which becomes "1" when the PIO accesses the backplane bus and becomes "0" when the PIO does not access the backplane bus.

Therefore, when PIO is not used, C
A control signal of "0" is sent from PU to the D terminal of the DQ flip-flop. As a result, the Q terminal output of the DQ flip-flop becomes "L", the second transistor Tr2 is turned off, and therefore the first transistor Tr1 is also turned off. Therefore, the power supply side terminal of the PIO is open. That is, the power supply voltage V _CC is not supplied to the power supply side terminal of the pull-up resistor R _P of the PIO that does not access the backplane bus.

On the other hand, when using PIO, the CPU sends a control signal of "1" to the D terminal of the DQ flip-flop. As a result, the Q terminal output of the DQ flip-flop becomes "H", the second transistor Tr2 is turned on, and therefore the first transistor Tr1 is also turned on. Therefore, P
The IO power supply side terminal is connected to the power supply. That is, the power supply voltage V _CC is supplied to the power supply side terminal of the pull-up resistor R _P of the PIO that accesses the backplane bus.

[0018]

As described above, according to the present invention, the supply of the power supply voltage is controlled based on the information as to whether the input / output module accesses the backplane bus. Even if there are a plurality of input / output modules to be processed, a plurality of input / output modules can be connected on the same backplane and transmission / reception and control operations can be performed between the input / output modules without increasing the load on the bus driver.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional configuration when connecting a plurality of input / output modules.

[Explanation of symbols]

OCD ... Open collector output type driver, R _P ... Pull-up resistor, Tr, Tr1, Tr2 ... Transistor, RG ...
register.

Claims (1)

[Claims] 1. A switching device used when a plurality of input / output modules including an open collector output type driver and a pull-up resistor are connected to the same bus, wherein each input / output module is connected to another via the bus. The input / output module switching device is configured to switch power supply to a power supply side terminal of a pull-up resistor of the input / output module depending on whether or not to access the input / output module.