Organization of banks
Each I/O digital bank has a total of 24 I/O lines connected to a 26-pin header. The
lines are configured into three groups: ports A, B and C, each group consisting of 8
bits. Any of the lines at ports A, B or C can be configured individually as inputs or
outputs.
Figure 9–2
Organization of banks
J14, Digital I/O 1
For J6, Digital I/O 2,
addresses are 124h
through 127h
8
8
8
Port C
Port B
Port A
Control
Register
Base
120h or
124h
Base + 1
121h or
125h
Base + 2
122h or
126h
Base + 3
123h or
127h
Port addressing
Ports A, B, C and the control register are addressable. The base I/O address for I/O
1 is fixed at 120h. The base address for I/O 2 is fixed at 124h. Ports A, B, C and the
control register are addressable, with reference to the base address.
I/O lines pulled low
The I/O lines at ports A, B, and C are always pulled low. This allows a known state
upon powerup. 10K ohm resistor networks are used to configure the I/O lines as
low.
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