Posted By
IstvanV
on 2007-11-14
05:40:59
|  Re: +4 UserPort
You cannot control if the lines are input or output, since they are always both. Basically, for each line there is a pull-up resistor connected to +5V, and a transistor pulls the output down when it should be 0V. The output current is low, so you may want to buffer it rather than driving relays etc. directly. For input, you would use a 7406 or similar open collector device. A few simple examples of controlling the user port from the monitor:
>FD10 FF makes all lines high (+5V)
>FD10 00 all are low (0V)
>FD10 01 P0 is high, all others are low
>FD10 80 P7 is high, all others are low
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