MITSUBISHI MICROCOMPUTERS
M37754M8C-XXXGP, M37754M8C-XXXHP
M37754S4CGP, M37754S4CHP
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Figure 5 shows basic waveforms of the bus interface unit. The RD
(BYTE) to “L” (external data bus width = 16 bits). The internal
memory area is always treated as 16-bit bus width regardless of
BYTE.
signal becomes “L” when the bus interface unit reads an instruction
___
code or data from memory. The WR signal becomes “L” when the
bus interface unit writes data to memory.
When performing 16-bit data read or write, if the conditions for simul-
taneously accessing two bytes are not satisfied, waveforms (2) and
(4) are used to access each byte, one by one.
Waveforms (1) and (3) in Figure 5 are used to access a single byte
or two bytes simultaneously. To read or write two bytes simulta-
neously, the first address accessed must be even. Furthermore,
when accessing an external memory area in memory expansion
mode or microprocessor mode, set the bus width select input pin
However, when prefetching the instruction code, if the address of the
instruction code is odd, only one byte is read in the instruction queue
buffer.
(1)
(2)
WR
RD
WR
RD
Internal address
bus
Internal address
bus
Address
Address (odd)
Address (even)
(A0 – A23)
(A0 – A23)
Internal data bus
(D0 – D7)
Internal data bus
(D0 – D7)
Data (even)
Invalid data
Data (even)
Internal data bus
(D8 – D15)
Internal data bus
(D8 – D15)
Data (odd)
Data (odd)
Invalid data
(3)
(4)
WR
WR
RD
RD
Internal address
bus
Internal address
bus
Address
Address (odd)
Address (even)
(A0 – A23)
(A0 – A23)
Internal data bus
(D0 – D7)
Internal data bus
(D0 – D7)
Data (even)
Data (odd)
Invalid data
Data (odd)
Data (even)
Invalid data
Internal data bus
(D8 – D15)
Internal data bus
(D8 – D15)
Fig. 5 Basic waveforms of bus interface unit
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RENESAS [ RENESAS TECHNOLOGY CORP ]
