Epson PX-8 Technical Manual page 54

REV.-A
2.3.1 Handshaking Between Main CPU and Sub-CPUs
The three CPUs operate using a clock supplied from a gate array (GAH40D), which has a built-in
frequency divider circuit. Data and commands are exchanged between the main CPU and the two
sub-CPUs as follow:
l
Gate
•
Main CPU
K
P,,,lIelt,,",'e, )
II \
(l80)
array
Serial transfer
1\ J
Sub-CPU 7508
GAH40M
,
"
'4
...
~~I
I
QjID
-
....
- r J )
~
C
co co
<;-.-?-
I
LCD controller
Gate array
....
f.E----
SED1320
.....
GAH40D
..c::;:
~
]1~
- r J )
~
C
COCO
0..;-
~7'1t
Slave CPU 6303
Data exchange between l80 and 6303: Handshaking is accomplished via the LCD controller.
Data exchange between l80 and 7508: Handshaking is accomplished via the gate array GAH40M.
Fig.2-25 Data/Command Exchange Between Main CPU and Sub-CPUs
2.3.1.1 Data/Command Exchange Between Main CPU and Sub-CPU 7508 via GAH40M
Commands are transferred in parallell between the main CPU and gate array and serially between
the gate array and sub-CPU 7508. Handshaking among the CPUs is performed via the read/write
control on the serial/parallel conversion register in the gate array. Fig. 2-26 illustrates this control.
Main CPU
Gate array (GAH40M)
Sub CPU
l-80
l;1
1\ ......-
Sl
so
7508
8-bit data bus
.\ SID
f\
vi
R CK
so
S1;.,
•
14: SCK
...
...
L-W
IT~
P20
. .
P22
..
.~
--.
I/O resistor
P21
~
CS
06 R
7001
~
SI
L----
so
I
Fig. 2-26 Main CPU and 7508 Handshaking Control
2-30