Apple Lisa - Page 30

Confidential Lisa Hardware Reference Manual
The
CO bus (bits COO to C07 above) can send commands to the COPS.
co COMMANDS
C07-CDO
Function
0000 0000
Turn I/O port on
0000 0001
Turn I/O port off
0000 0010
Read clock da ta
0001
nnnn Write nnnn to clock
0010 spmm Set clock modes (see Clock below)
0011 nnnn
Write nnnn to low indicator bits in keyboard
0100 nnnn Write nnnn to high indicator bits in keyboard
0101 nnnn
Set high nibble of NMI character to nnnn
0110 nnnn
Set low nibble of NMI character to nnnn
lxxx x::ooc Do nothing (null command)
If the 6522 is not programmed as an output when the CRDY line
makes a high to low transition (thereby indicating that the COPS
is ready to accept a command), the pullup on the CO bus prevents
a spurious command from being entered.
The pin description given above indicates that the CO bus (the
Peripheral A Port) should be set up to handshake and to latch data.
If the 6522 is set up correctly, when the I/O board COPS has data
for the 6S000 it will handshake with the handshake lines and
generate an interrupt.
The indicator bits can be used to control 8 LEDs. If, for example,
these LEDs are installed on the keyboard, they can be used to emulate
a VT-lOO terminal.
Page 30
7-Jul-Sl