THE PIA (6532)

4.0 The I-O ports

The two ports (Port A and Port B) are 8 bits wide and can be set for either input or output. Port A is used to interface to carious hand-held controllers but Port B is dedicated to reading the status of the Stella console switches.

4.1 Port B - Console Switches (read only)

Port B is hardwired to be an input port only that is read by addressing SWCHB (HEX 282) to determine the status of all the console switches according to the following table:

          Data Bit  Switch         Bit Meaning
          D7        P1 difficulty  0 = amateur (B), 1 = pro (A)
          D6        P0 difficulty       0 = amateur (B), 1 = pro
          (A)
          D5/D4          (not used)
          D3        color - B/W    0 = B/W, 1 = color
          D2        (not used)
          D1        game select    0 = switch pressed
          D0        game reset     0 = switch pressed

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