Page 12
Operation of the Card
Page 12
01270146.doc
Blue Chip Technology Ltd.
OPERATION OF THE CARD
Programmable Digital Input/Outputs
The AOP-12d includes an NEC µPD71055 device which is equivalent to an
Intel 8255 PIO.
This device provides 24 programmable digital I/O channels. It is suitable for
sensing the presence of, or driving TTL connections only. These connections
should be kept as short as possible, less than 2 metres is recommended.
The digital I/O appears to the PC as four ports. The first three can be set as
input or output by writing suitable codes to the fourth Control Port.
These four ports are mapped into the AOP-12d address map as follows:
BASE
+ 4
Programmable Digital I/O Port A (read/write);
+ 5
Programmable Digital I/O Port B (read/write);
+ 6
Programmable Digital I/O Port C (read/write);
+ 7
Control Port (write only).
A summary of the codes required to change the operation of the ports are given
later. A typical sequence of events to use this feature would be :
•
Decide on the input/output mix and write the appropriate code to
BASE + 7.
•
Read from the selected output port or write to the selected output port.
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