Digital I/ O prog ramm ing exam ple

DIGITAL AND OPTO PORTS

Protection diodes m ust be used with inductive loads. Refer to figure 6-2

Figure 6-2 Inductive load protection

Do not pa rallel outputs f or higher drive. This could result in damage since outputs will not share current equally.

The outputs at U12 are open collector. An external device must supply power .

Interfacing Digital I/O to an opto-module rack

I/O lines at J3 can interface to an MPS-8, 16, or 24 position opto m odule 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 series modules.

ACM A-26-24 connects J3 on the RPC-320 to the MP S- XX bo ard. Cable len gth should be less than 2 feet. Excessive cable lengths cause a voltage drop and consequently unreliable operation. Make sure + 5 V and ground is connected to the M PS-XX racks.

Before a line is set, the 82C55 chip must be initialized. This is done using the CONFIG LINE statement. Group inputs and outpu ts together. Refer to Table 6-1 for opto module position, port number , and connector pin out. If opto channels 16-23 are used, U12 should be replaced by a DIP shunt jumper .

The LINE and LINE # com mands are used to control and access opto modules and lines. These commands are both functions and statements, depending upon how they are used.

100	LINE 100, 0	Statement
110	LINE #103, 0	Statement
120	A = LINE(100)	Function

SECTION 6

130

A = LINE#(103)

Function

Program line 100 turns external opto module rack position 0 off. Program line 110 sets J3, pin 3, to a logical 0 level. Program line 120 returns the status of externa l opto modu le rack po sition 0. If the modu le is "off", a 1 is returned (assuming it is an output module). Program line 130 returns the status of J3, pin 3 as a 0 or 1.

Example: To turn on opto module in slot position 8, the following command is executed:

LINE 108, 1

A ' 1' turns on a module while a 0 turns it off. (In actual fact, a 0 is written at the port. )

See Digital I/ O program ming exam ple later in this chapter .

Interfacing to switches and other devices

Switches and other digital I/O devices may be connected directly to P6 or J3 . The STB - 26 terminal board provides a convenient way of interfacing switches or other digital I/ O device s. L ines at J3 are connected to the STB -26 with a CMA - 26 cable . Digital devices are then connected to the screw terminals on the STB-26. The M PS-X X serie s opto rac ks also pro vide a way to access digital I/O lines.

Switches may be connected directly to a line. When jumper W7 configures the resistors as pull ups, a switch closure to ground at a line is read as a 0 using the LINE

#function at J1. 10K resistors are always pulled up at lines L0 to L7.

When W 7 configures the input re sistors as pull downs, one end of the switch m ust be tied to + 5 volts. If this is not possible or convenient, a 1K resistor can be tied between an input and + 5 volts to force it high when a switch is open.

The follow ing exam ple read s a switch at po rt A, bit 3

(J3-25) (program line 200), r eads L1 at P6 (program line

210)and turns on opto module at channel 5 (program line 220). A LE D is controlled through the high current port at J3-10 (port B, bit 0) (program lines 230 and 240). For testing, a 100 ohm resistor from J3-10 to + 5 volts can be substituted.

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