Octagon 2060 PC/104, Справочное руководство

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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. Note that 10K ohm resistor networks are used to configure the I/O
lines as low.
Configuring and programming the I/O ports
The I/O chip has three ports with eight parallel I/O lines (bits) per port. All lines
can be individually programmed as all inputs, all outputs or individually as inputs
or outputs. You can alter which bits are inputs or outputs by writing a control
command to the control register. When a line is configured as an output, it can
sink a maximum of 15 mA at 0.4V or can source 15 mA at 2.4V. On powerup and
software or hardware reset, all digital I/O lines are reset as inputs.
Programming the I/O
Follow these steps to program the I/O chip:
1. Configure the I/O port bit directions, either as inputs or outputs.
2. Write to port A, B, or C with the desired level or read the bit level from the
desired port.
Configuring the I/O
Follow these steps to configure the I/O chip.
Note In the following examples, “base” for I/O always refers to the starting address
selected in Setup (120h default).
1. Write a “2” to the control register (base a 3). This places the I/O chip
in “direction” mode: (base address = 120h)
OUT 123h, 2 (control register, direction mode)
2. Set the direction of each bit. A “0” written to the corresponding line indicates
an input and a “1” bit indicates an output. Each bit corresponds to the
equivalent I/O line.
Table 10–4 Digital I/O port byte
Bit
7 Bit
6 Bit
5 Bit
4 Bit
3 Bit
2 Bit
1 Bit
0 Port I/O
Line
X 7
X 6
X 5
X 4
X 3
X 2
X 1
X 0
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