4
J206 PCIB40 Technical Manual
2192-09066-000-000
Operation
Reading or Writing to the Board
Control of the PCIB40 is achieved by writing to a pointer register and then accessing a data
register to read or write the required I/O register. The pointer register need only be written with a
new value if a different register is to be accessed. The board occupies only two bytes of PCbus
I/O space. Each time the board is accessed, the red LED will flash momentarily.
Digital I/O channels
To use a digital channel (or bit) as an output simply write to that channel (or bit). To use a digital
channel (or bit) as an input write a ‘1’ to the channel to initialise . Thereafter a read can be used.
You can configure each digital channel (or bit) as an input or an output but it is advisable to
configure the board in groups. e.g. Group 1,2 & 3 output, Group 4 & 5 input. When an output is set
to ‘0’ (logic low) it is not advisable to attempt to drive the external connection to logic high.
Reading a digital channel, when it is an output, will return the state of the output. This can be useful
if you need to check the status of an output.
Electrical configuration of each digital channel:
Power-up or reset state of outputs
When digital I/O boards are used to control large or crucial items of plant, it is often necessary to
define how the output lines power-up. This is because it can take many seconds to boot an
operating System and run an application program from reset and begin initialising the system.
Each group of eight I/O signals can be selected to be a logical ‘0’, a logical ‘1’ or ‘don’t care’ at
power-up or on reset. This is configured using jumpers (see links section).
To use this feature set the links for the power-up or reset condition required. Then in your code
write to the group registers the output levels required, and finally enable the outputs by writing a
‘1’ to bit 0 of register 90 (hex).
Note: This feature is suited to outputs not inputs. Setting an input to a power-up state of ‘0’ will
require the group register being written with all ‘1’s’ to enable the use of the channels as inputs.
Read Status
Write Control
Data
Power-Up State
A
B
From output Enable latch
Enable
D
Q
+5V
4K7
10K
I/O Signal
Output Enable Software/Always
(Common to 8 I/O Channels).
A
B
(Common to 8 I/O Channels).
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