Kontron 104-AD128, User Manual

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5-8
104-ADIO128 (AD128) User’s Guide
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Using Digital Input/Output Ports
This circuit is based on an 82C55A chip. Please refer to file 82C55.pdf in the \CHIPDOCS
directory.
On power-up or on Reset the circuit will be in the mode 0 input state. That is, ports A and B (each
8 bits) and ports C ‘upper’ and C ‘lower’ (each 4 bits) will be readable and any floating pins at
connector P4 will be high.
Table 5-2. Digital I/O Command-Byte
To change Port A and Port B I/O configuration, there are two modes. In the default mode the
buffers’ direction is automatically set by the command-byte. This mode is designed to support
‘off the shelf’ software.
Bit Description Function
Bit 0 Port C Direction 1 = Input
0 = Output
Bit 1 Port B Direction 1 = Input
0 = Output
Bit 2 Group B Mode 1 = Mode 1
0 = Mode 0
Bit 3 Port C Upper Direction 1 = Input
0 = Output
Bit 4 Port A Direction 1 = Input
0 = Output
Bit 5 Group A Mode 1 = Mode 1
0 = Mode 0
Bit 6 Group A Mode 1 = Mode 2
0 = use Bit 5
Bit 7 Mode Set Flag 1 = Active