Bus
34
Mitsubishi microcomputers
M16C / 62P Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
development
Preliminary Specifications Rev.1.0
Specifications in this manual are tentative and subject to change.
Function
Bit symbol
Bit name
Chip select control register
Symbol
CSR
Address
0008
16
After reset
00000001
2
RW
b7
b6
b5
b4
b3
b2
b1
b0
CS1
CS0
CS3
CS2
CS0 output enable bit
CS1 output enable bit
CS2 output enable bit
CS3 output enable bit
CS1W
CS0W
CS3W
CS2W
CS0 wait bit
CS1 wait bit
CS2 wait bit
CS3 wait bit
0 : Chip select output disabled
(functions as I/O port)
1 : Chip select output enabled
0 : With wait state
1 : Without wait state
(Note 1, Note 2, Note 3)
RW
RW
RW
RW
RW
RW
RW
RW
Note 1: Where the RDY signal is used in the area indicated by CSi (i = 0 to 3) or the multiplex bus is used, set
the CSiW bit to “0” (Wait state).
Note 2: If the PM17 bit in the PM1 register is set to “1” (with wait state), the external area indicated by CS0 to
CS3 is always accessed with one wait state even when the CSiW bit is “1” (without wait state).
Note 3: When the CSiW bit = “0” (with wait state), the number of wait states (interms of clock cycles) can be
selected using the CSEi1W to CSEi0W bits in the CSE register.
Figure 1.7.1. CSR Register
Bus Control
The following describes the signals needed for accessing external devices and the functionality of software
wait.
(1) Address Bus
The address bus consists of 20 lines, A
0
to A
19
. The address bus width can be chosen to be 12, 16 or
20 bits by using the PM06 bit in the PM0 register and the PM11 bit in the PM1 register. Table 1.7.1
shows the PM06 and PM11 bit set values and address bus widths.
When processor mode is changed from single-chip mode to memory extension mode, the address
bus is indeterminate until any external area is accessed.
(2) Data Bus
When input on the BYTE pin is high, 8 lines D
0
to D
7
comprise the data bus; when input on the BYTE
pin is low, 16 lines D
0
to D
15
comprise the data bus.
Do not change the input level on the BYTE pin while in operation.
(3) Chip Select Signal
The chip select (hereafter referred to as the CSi) signals are output from the CSi (i = 0 to 3) pins.
These pins can be chosen to function as I/O ports or as CS by using the CSi bit in the CSR register.
Figure 1.7.1 shows the CSR register.
During 1 Mbyte mode, the external area can be separated into up to 4 by the CSi signal which is output
from the CSi pin. During 4 Mbyte mode, CSi signal or bank number is output from the CSi pin. Refer to
“Memory space expansion function”. Figure 1.7.2 shows the example of address bus and CSi signal
output in 1 Mbyte mode.
Set value(Note)
PM11=1
PM06=1
PM11=0
PM06=1
PM11=0
PM06=0
Note 1: No values other than those shown above can be set.
Pin function
P3
4
to P3
7
P4
0
to
P43
A
12
to
A15
P4
0
to
P43
A
12
to
A15
A
16
to
A19
Address bus wide
12 bits
16 bits
20 bits
Table 1.7.1. PM06 and PM11 Bits Set Value and Address Bus Width