deveopmen
Rev.B2 for proof reading
Bus Control
Mitsubishi Microcomputers
M32C/83 group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
61
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
H
H
L
H
L
Not used
CASL
L
L
L
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 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
(10) Software wait
A software wait can be inserted by setting the wait control register (address 0008
16
). Figure 1.7.6 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.
SFR area is accessed with either "1 wait" (BCLK 2-cycle) or "2 waits" (BCLK 3-cycle) by setting the SFR
wait bit (bit 3) of the processor mode register 1 (address 0005
16
). SFR area of CAN must be accessed
with "2 waits".
Table 1.7.11 shows the software waits and bus cycles. Figures 1.7.7 and 1.7.8 show example bus timing
when using software waits.