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DIGITAL AND OPTO PORTS CHAPTER 6

Page 22 RPC-30

Figure 6-2 Inductive load protection

High current output

Eight lines at J3 can be used as high current driver s.

These outputs will switch loads to ground. Outputs are

controlled by Port B on the 82C55. Its address is 1.

Logic outputs are inverted. That is, when a 1 is written

to the high current port, the output is switched on and

goes low.

The output driver chip, U 1, can be replaced with a DIP

shunt jumper so it is like the other lines at J3.

NOTE: Outputs at the high current lines are not

compatible with TT L logic levels and should

not be used to drive other logic devices.

Each of the high current outputs can sink 100 ma at 50V.

WARNING:

External supplies using the high current outputs must

be tied to J3, pin 26 and NOT the power connector.

Failure to do so can produce a ground loop and

cause erratic operation.

The ther mal time constant of the package is very short,

so the number of outputs that are on at any one time

should include those that overlap even for a few

milliseconds.

Incandescent lamps have a "cold" current of 11 times its

operating current. Lamps requiring more than 50 ma

should not be used.

Protection diodes m ust be used with inductive loads.

Refer to figure 6-2

Do not parallel outputs for higher drive. This could

result in damage since outputs will not share current

equally.

Interfacing to an opto-module rack

I/O lines can be interfaced to an MPS-8, 16, or 24

position opto module rac k. L ines not going to an opto

module connect to a screw terminal on the MPS-XX

series boards. This feature allows you to connect

switches or other TTL type devices to the digital I/O

lines. The MPS-XX series boards accept G4 and G5

series modules.

Use the O PTO comm and to access and control G4 opto

modules. The LIN E comm and is used to access

individual lines on the STB-26. Add 100 to any LINE

command to access pins on the STB-26. For example,

LINE(103) reads pin 3 at J3.

A CMA-26 connects J3 on the RPC-30 to the MPS-XX

board. Cable length should be less than 2 feet for the 8

position rack and 18 inches for the 16 and 24 positions.

Excessive cable lengths will cause a high voltage drop

and consequently unreliable operation. Make sure you

connect ground and + 5V to the opto racks.

Use the following table to determine the corresponding

opto channel for a par ticular 82C 55 port:

Opto 82C55 J3

channels port Address

0-3 Lower C 2

4-7 Upper C 2

8-15 A 0

16-23 B 1

To turn on an opto module, a line must be low. A

module is turned off by writing a ' 1' to a channel. The

logic at port B, with the high current outputs installed is

just the reverse. A ' 1' at a line causes the module to

turn ON.

High cur rent outputs at port B are optionally

configurable as TTL I/O by replacing U1 with a DIP

shunt jumper. This will keep the logic com patible with

ports A and C. If opto channels 16-23 are used as

inputs, then U1 must be replaced by a DIP shunt jumper.

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 ... 37 38

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