Remote Processing RPC-52 - Manual (Page 20)

DIGITAL AND OPTO PORTS CHAPTER 6
Page 18
Figure 6-2 Inductive load protection
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
outputs sink 15 m a at 1. 0V. This will dr ive opto
modules. P ort B is connected to a high current sink
through U 20. See "H igh curr ent output" later in this
chapter.
Digital I/O lines at J4 are pulled up to + 5 volts or
ground through a 10K resistor pack using jumper W 9.
Jumper W9 for pull up or down configuration is as
follows:
W9[1-2] Pull up
W9[2-3] Pull down
Setting W9 for pull up makes interfacing to switches and
"open collector" TTL devices easy . See "Inter facing to
Switches and other devices" below.
Digital I/O commands
The CO NFIG LINE statement is used to configure the
82C55 ports. This statement stores input and output
parameters in serial EE PROM for recall at power up or
reset. CON FIG LINE should not be executed very often
as the seria l EEP ROM has a limited n umber of write
cycles (100, 000). F actory default is: P ort A - Inputs,
Port B - Outputs, Port C - Inputs.
LINE function and statement is used with opto m odules.
It accesses a module according to the position number
printed on the board . L ines are n umber ed from 100 to
123. The opto m odule num ber used in this comm and is
computed by adding 100 to the board position number.
The LIN E B function and statement is used to acc ess
digital I/O lines 8 bits at a time . T he addr ess for po rt A
is 0, B is 1, and C is 2. The bank number is 3.
LINE # function and statement accesses lines according
to the pin number at J4. Lines are num bered from 101
to 125. The line nu mber used in this com mand is
computed by adding 100 to the connector pin number.
Line 102 is not allowed as it is the + 5V supply. See
table 6-1 to cor respond a pin numb er to a por t and opto
rack position.
LIN E, LINE B and LIN E # re turn the ' true' logic level.
A ' 1' indicates + 5 volts or high and a '0' is low or
ground. LINE B and LINE # output true logic levels.
LINE, however, outputs inverted logic. In order to turn
on an opto module, a line must go low. However,
turning on a module using LINE, you must specify a
' 1' .
High current output
Eight lines at J4 can be used as high cur rent driver s.
These outputs will switch loads to ground. Outputs are
controlled by Port B on the 82C55.
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 20, can be replaced w ith a DIP
shunt jumper so it is like the other lines at J4.
NOTE: Outputs at the high current lines are not
compatible with TTL logic levels and should not
be used to drive other logic devices.
Each of the high current outputs can sink 500 ma at 50V.
How ever, package diss ipation will be ex ceeded if all
outputs are used at the maximum rating. The following
conserv ative guidelines a ssume the number of outputs
are on simultaneously:
# of outputs Maximum current
on per output
1 5 0 0 m a
2 4 0 0 m a
3 2 7 5 m a
4 2 0 0 m a
5 1 6 0 m a
6 1 3 5 m a
7 1 2 0 m a
8 1 0 0 m a
The ther mal time constant of the p ackage is ve ry shor t,
s o th e nu m b er o f o u tp u ts th a t a r e on a t a n y o n e t im e
should include those that overlap even for a few
milliseconds.
Incandesc ent lamps h ave a " cold" c urre nt of 11 times its
o p er a ti ng c ur r e nt . L a m ps r eq u ir i ng m o re th a n 5 0 m a
should not be used.
Protection diodes m ust be used with inductive loads.
Refer to figure 6-2
Do not pa rallel outputs f or higher drive. This re sults in
damage since outputs do not share current equally.
The outputs at U20 are pulled either up or down through
10K resistors, according to the status of jumper block
W9.
Interfacing digital I/O to an opto-module rack
I/O lines can be interfaced 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
s w it ch e s o r ot he r T T L t yp e de v ic e s t o t he d ig it al I/ O