Table 10–4 Digital I/O port addressing
I/O 1 base address
I/O port
Port I/O address
120h* A
Base
address
180h**
B
Base a 1
320h**
C
Base a 2
380h**
Control Register
Base a 3
I/O 2 base address
I/O port
Port I/O address
124h* A
Base
address
184h**
B
Base a 1
324h**
C
Base a 2
384h**
Control Register
Base a 3
* = default
** = selected in Setup
Base I/O address
The default base I/O address for digital I/O1 is 120h and is 124h for
digital I/O2.
Digital I/O1 always uses [base through base +3], and digital I/O2 uses
[base + 4 through base + 7]. Ports A, B, C and the control register are
addressable, with reference to the base address. These addresses can be
changed through Setup to one of four addresses.
Pulling the I/O lines high or low
Jumper blocks W2 and W4 pull the I/O lines at ports A, B, and C high or
low. This allows a known state upon power-up. The default configuration
pulls all of the I/O lines high. Note that 10K ohm resistor networks are
used to configure the I/O lines as high or low.
Table 10–5 Digital I/O pull-up/pull-down jumpers: W2 and W4
W2, W4 –I/O pull-up/pull-down jumpers
I/O Lines
Pull UP (+5V)
Pull DOWN Gnd)
0-7 W2[2–4]*
W2[4–6]
I/O
8-15 W2[1–3]* W2[3–5]
Bank 1
16-23 W2[9–10]* W2[7–9]
0-7 W4[2–4]*
W4[4–6]
I/O
8-15 W4[1–3]* W4[3–5]
Bank 2
16-23 W4[9–10]* W4[7–9]
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