M38067M2AFP datasheet(32/58 Pages) RENESAS

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MITSUBISHI MICROCOMPUTERS

3806 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

Bus control with memory expansion

_____

The 3806 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.

_____

Fig. 30 ONW function timing

Read cycle

Write cycle

Dummy cycle Write cycle

Read cycle Dummy cycle

AD15 to AD0

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.

V :

ONW

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