Epson PX-8 Technical Manual page 295

(5) I/O port
Power supply for the RS-232C, memory bank
switching, and LED display on keyboard are
controlled through the I/O port.
(RS-232C)
Fig. 7-10 controls power increases
The bits 3 and 4 of I/O address 02H.
±
8V output is controled by the INHRS signal,
and is performed in order to inhibit output
INHRS I---~
-8V
1-----....._
voltage on the line during saturation time.
+8V
1-----
(Bank switch)
±8VOUTPUT
j
REV.-A
Fig. 7-10
The address space of the main CPU can be changed using bit 0 of I/O address OOH as shown be-
low.
OOH bit 0
=
OFF (Bank 0) ROM
RAM
OOOOH
8000H FFFH
OOH bit 0
=
ON (Bank 1)
I
RAM
I
RAM
I
Fig. 7-11
(LED display)
ON/OFF operation of shift mode LED on the keyboard is controlled using bits 0 to 2 of address
02H. (Bit ON drives the corresponding LED.)
7-24