M38027E8SP Datasheet, PDF (32/51 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

Bus control with memory expansion
The 3802 group has a built-in ONW function to facilitate access to
external memory and I/O devices in memory expansion mode or
microprocessor mode.
If an “L” level signal is input to the ONW pin when the CPU is in a
read or write state, the corresponding read or write cycle is ex-
tended by one cycle of φ. During this extended period, the RD or
WR signal remains at “L”. This extension period is valid only for
writing to and reading from addresses 000016 to 000716 and
044016 to FFFF16 in microprocessor mode, 044016 to YYYY16 in
memory expansion mode, and only read and write cycles are ex-
tended.
MITSUBISHI MICROCOMPUTERS
3802 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
Read cycle
Dummy cycle Write cycle Read cycle Dummy cycle
Write cycle
φ
AD15 to AD0
RD
WR
ONW
V
V
V
V : Period during which ONW input signal is received
During this period, the ONW signal must be fixed at either “H” or “L”. At all other times, the input level of the ONW
signal has no affect on operations.
The bus cycles is not extended for an address in the area 000816 to 043F16, regardless of whether the ONW signal
is received.
Fig. 34 ONW function timing
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