UPD784020 Datasheet, PDF (49/90 Pages) NEC – 16/8-BIT SINGLE-CHIP MICROCOMPUTER

mPD784020, 784021
10. LOCAL BUS INTERFACE
The local bus interface enables the connection of external memory and I/O devices (memory-mapped I/O). It
supports a 1M-byte memory space. (See Fig. 10-1.)
Fig. 10-1 Example of Local Bus Interface
µPD784021
A16-A19
RD
WR
REFRQ
Pseudo SRAM
PROM
µ PD27C1001A
Kanji character
generator
µPD24C1000
AD0-AD7
DDaattaabbuuss
ASTB
A8-A15
Latch
Address bus
Gate array for I/O
expansion including
Centronics interface
circuit, etc.
10.1 MEMORY EXPANSION
By adding external memory, program memory or data memory can be expanded, 64K bytes at a time, to
approximately 1M byte (three steps).
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