deveopmen
Bus Control
Preliminary Specifications REV.B
Specifications in this manual are tentative and subject to change.
Mitsubishi microcomputers
M16C/80 (144-pin version) group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
36
(10) Software wait
A software wait can be inserted by setting the wait bit (bit 7) of the processor mode register 1 (address
0005
16
) (Note) and bits 4 to 7 of the wait control register (address 0008
16
). Figure 1.7.5 shows wait
control register
You can use the external area I wait bits (where I = 0 to 3) of the wait control register to specify from “No
wait” to “3 waits” for the external memory area. When you select “No wait”, the read cycle is executed in
the BCLK1 cycle. The write cycle is executed in the BCLK2 cycle (which has 1 wait). When accessing
external memory using the multiplex bus, access has two waits regardless of whether you specify “No
wait” or “1 wait” in the appropriate external area i wait bits in the wait control register.
Software waits in the internal memory (internal RAM and internal ROM) can be set using the internal
memory wait bits of the processor mode register 1 (address 0005
16
). Setting the internal memory wait bit
= “0” sets “No wait”. Setting the internal memory wait bit = “1” specifies a wait.
The SFR area is not affected by the setting of the internal memory wait bit and is always accessed in the
BCLK2 cycle.
Table 1.7.11 shows the software waits and bus cycles. Figures 1.7.6 and 1.7.7 show example bus
timings when using software waits.
Status of external data bus
Read data from both even and odd addresses
Read 1 byte of data from even address
Read 1 byte of data from odd address
Write data to both even and odd addresses
Write 1 byte of data to even address
Write 1 byte of data to odd address
Read 1 byte of data
Write 1 byte of data
RAS
L
L
L
L
L
L
L
L
CASH
L
L
H
L
H
L
Not used
CASL
L
L
H
L
L
H
L
L
Data bus width
DW
H
H
H
L
L
L
H
L
8-bit
16-bit
Not used
(9) DRAM controller signals (RAS, CASL, CASH, and DW)
Bits 1, 2, and 3 of the DRAM control register (address 0004
16
) select the DRAM space and enable the
DRAM controller. The DRAM controller signals are then output when the DRAM area is accessed. Table
1.7.10 shows the operation of the respective signals.
Table 1.7.10. Operation of RAS, CASL, CASH, and DW signals