Epson PX-8 Technical Manual page 56

REV.-A
As can be learned from the figure, the handshake is accomplished via the SID READY signal as
follows:
{
When SID READY is set
When SID READY is reset
Z80
7508
---+GAH40M
---+GAH40M
The SID READY signal is set and reset by the following signals:
SID READY is reset when READY FF is reset by bit 0 of Z80 I/O address 01.
SID READY is set by 7508 port 22 .
• The SID READY signal is set and reset either by a command (data) or interrupt. The operations
are illustrated by Fig. 2-28
Command (data)
START
Write command
and reset SID FF.
Termination
N
N
Write or read
command.
Reset SID FF.
Interrupt
START
Read status and
reset SID FF.
Read status.
Check status
(to determine
interrupt type).
y
Fig. 2-28 Main CPU and Sub-CPU Interfacing Operations
2-32
Enter data from
keyboard.