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DIGITAL LINES CHAPTER 6

Page 16 RPC-2300

Figure 6-1 Digital I/O

INTRODUCTION

Digital I/O lines ar e used to inter face with opto-module

racks, switches, low current LED's, and other TTL

devices. The SBS-2300 has 48 of these lines available

through J2 and J3. Eight of these lines are high current

outputs, capable of sinking 75 to 200 ma. Eight lines on

J3 are shared by the keypad connector, J5. When the

keypad is used, 8 of the 48 lines are not available.

Eight, 16, or 24 position opto racks are connected to J2

or J3. These opto racks accept G4 ser ies opto modules.

G4 series opto modules are used to sense the presence of

AC or D C voltages or switch them. Maximum

switching current is 3 amperes.

WARNING:

Apply power to the SBS-2300 before applying a

voltage to the digital I/O lines to prevent current

from flowing in and damaging devices. If you

cannot apply power to the SBS-2300 first, contact

technical support for suggestions appropriate to your

application.

DIGITAL I/O PORT

Digital I/O lines on the SBS-2300 are supplied by an

82C55 chip. The chip' s lines go to connectors J2 and

J3.

The lines on J2 and J3 are divided into 3 eight bit

groups. Ports A and B can be configured as all inputs or

outputs. Port C can be programm ed as one group of 8

inputs or outputs or as two groups of four lines (upper

and lower C). The four lines in upper and lower C can

each be progr ammed as all inputs or outputs.

When a line is configured as an output, it can sink a

maximum of 2. 5 mA at 0. 4V and can source over 2. 5

mA at 2.4V. Outputs sink 15 mA at 1.0V.

J2 and J3 are accessed using CAMBASIC II LINE,

OPTO, INP, and OUT statements. LINE r eads or

writes to a port based on the connector num ber. LINE is

generally used with the STB-26 board. OP TO reads or

writes to an opto module based on its position in an MPS

opto rack. IN P and O UT a ccess a byte o f data at a por t.

The base I/O address for J2 is 0 and J3 is 64 when using

INP, OUT, and CONFIG PIO statements. CONFIG

PIO statement is used to configure the 8255 lines for

inputs and outputs. Upon reset, lines are configured for

inputs.

J2 and J3 are accessed using LIN E or O PTO statements

according to the table below.

Connector LINE # OPTO rack

No terminal position

J2 1-25 0-23

J3 101 - 125 100 - 123

LINE #' s access that pin number on J2 or J3. LIN E # 2

or 102 are not valid. Line 2 is + 5 volt supply.

J3, port A is connected to a high current sink through

U20. See High current output later in this chapter.

J3 port C is shared with the keypad port J5. If you are

using a keypad through J5, these 8 lines are not

available.

Pull up resistors

Digital I/O lines at J2 and J3 are pulled up to + 5 volts

through a 10K resistor pack.

These pull ups makes interfacing to switches and "open

collector" TTL devices easy . See "Inter facing to

Switches and other devices" below.

High current output

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

These outputs switch loads to ground. Outputs are

controlled by Port A on the 82C55. Its address is 64.

Logic outputs from this port are inverted. That is, when

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 35 36

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