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