Epson PX-8 Technical Manual page 294

REV.-A
(4) 7508 interface
The 7508 interface contains the circuitry for handshaking between the parallel-serial converting
register on the main CPU and 7508.
SI
SO 7508
~
Vt
~
SIOR
SCK
~
V
....
-
I~
Parallel-
Main
serial
CPU
register
I SO
...
SI
...
Y
ROYSIO
-
DFFQ
INTS
CKRSQ
INT1
I
ROY
P22
Fig. 7-9
Handshaking is performed in the internal flip-flop. When it is set, it means that the main CPU can
access SIOA. When it is reset, it means that an interrupt signal is sent to the 7508 and the com-
mand set at SIOR is read by the 7508. The internal flip-flop is controlled by bits 0 and 1 of ad-
dress OIH.
After the R/W operation to/from SIOR is completed, the set status must be changed by writing to
address OIH.
Table 7-8
Address OIH Reset The main CPU sets a command to SIOR
Bit 1 RDYSIO
and requests processing to 7508.
Address OIH Set The power is turned on and access to
BitO
RDYSIO 7508 is completed.
7-23