
Specifications in this manual are tentative and subject to change
Rev. E
MITSUBISHI MICROCOMPUTERS
M30245 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
30
Processor Mode
Bus Control
The following explains the signals required for accessing external devices and software waits. The
signals required for accessing the external devices are valid when the processor mode is set to memory
expansion mode and microprocessor mode. The software waits are valid in all processor modes.
Address bus/data bus
The address bus consists of the 20 pins A0 to A19 for accessing the 1M bytes of address space.
The data bus consists of the pins for data I/O. When the BYTE pin is “H”, the 8 ports (D0 to D7) function as
the data bus. When BYTE is “L”, the 16 ports (D0 to D15) function as the data bus.
When a change is made from single-chip mode to memory expansion mode, the value of the address bus is
undefined until external memory is accessed.
Chip select signal
The chip select signal is output using the same pins as P44 to P47. Bits 0 to 3 of the chip select control
register (address 000816) set each pin to function as an I/O port or to output the chip select signal. The chip
select control register is valid in memory expansion mode and microprocessor mode. In single-chip mode,
P44 to P47 function as programmable I/O ports regardless of the value in the chip select control register.
In microprocessor mode, only CS0 outputs the chip select signal after reset. CS1 to CS3 function as input
ports. Figure 1.13 shows the chip select control register.
The chip select signal can be used to split the external area into as many as four blocks. Table 1.16 shows
the external memory areas specified using the chip select signal.
Figure 1.13.
Chip-select control register
Bit Symbol
Function
R
W
Symbol
CSE
Address
001B
16
Chip select expansion register
Note :
These bits function normally only when the corresponding CSxW bit is "0". When CSxW bits
are set to "1", these bits must be returned to "00".
When reset
00
16
Bit Name
CSE0W
CSE1W
CSE2W
CSE3W
CS0 wait expansion bit
CS1 wait expansion bit
CS2 wait expansion bit
CS3 wait expansion bit
0 0 : CSxW setting enabled (x=0-3)
0 1 : 2 Wait states
1 0 : 3 Wait states
1 1 : Invalid
O
b7
b0
b6
b5
b4
b3
b2
b1
O
Bit Symbol
Function
R
W
Symbol
CSR
Address
0008
16
Chip select control register
When reset
01
16
Bit Name
CS0
CS1
CS2
CS3
CS0W
CS1W
CS2W
CS3W
CS0 output enable bit
CS1 output enable bit
CS2 output enable bit
CS3 output enable bit
CS0 wait bit
CS1 wait bit
CS2 wait bit
CS3 wait bit
0 : Chip select output disabled (Normal port pin)
1 : Chip select output enabled
O
b7
b0
b6
b5
b4
b3
b2
b1
O
0 : Wait state inserted
1 : No wait state
O