|54019|$D303|PBCTL|Port B Control|only A (400/800)

|7|PA7|Interrupt status of SIO
|6|PA6|always 0
|5|PA5|always 1
|4|PA4|always 1 
|3|PA3|Status of command line of SIO
|2|PA2|1=use Port B for data input/output, 0=define data direction, see below 
|1|PA1|always 0
|0|PA0|Interrupt of PROCEED line on/off, set to 0 by OS

To define the data direction of PORT B, set Bit 2 of [PBCTL] to 0. Then write a byte to [PORTB], where Bits set to 1 indicate WRITE and Bits set to 0 indicate READ. Normally [PORTB] is set to %00000000 (=all input).

see also: [Controller topics|Controller_topics]

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