Acces PAD128, User Manual

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Manual MPAD128.D1g
Digital I/O
The PAD128 comes with both analog inputs and digital I/O. Digital bits are provided
through an industry standard 8255 PPI chip. The 8255 is a powerful and flexible
solution to many digital needs, providing two eight-bit ports and two four-bit ports
individually selectable as input or output. Due to pinout restrictions, the PAD128
makes only ports A and B available at the connector. Port C-Low can be programmed
to control special various functions in the onboard logic device. If you are interested
in special functions please contact us.
The two 8-bit digital I/O ports that are available at the connector are controlled through
the 8255 device located at Base + 20 through Base + 23.
Programming Example
The following example in C is provided as a guide to assist you in developing your
working software. In this example, the card address is 2D0 hex, operation is in Mode
0 and the I/O lines are to be set up as follows:
Port A Input
Port B Output
Port C Hi Input (ignored)
Port C Lo Output (ignored, but usable for control functions in special
versions of the PAD128.
Configure bits of the control register as follows:
D7 D6 D5 D4 D3 D2 D1 D0
1 0 0 1 1 0 0 0
| | | | | | | |
| | | | | | | |__ Port C Lo = Output
| | | | | | |
| | | | | | |______Port B = Output
| | | | | |
| | | | | |__________ Mode 0
| | | | |
| | | | |_____________ Port C Hi = Input
| | | |
| | | |_________________ Port A = Input
| | |
| | |_____________________
| | } Mode 0
| |_________________________
|
|_____________________________ Active Mode Set