Epson PX-8 - 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