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M30245 Group
Processor Mode
Rev.2.00
Oct 16, 2006
page 30 of 264
REJ03B0005-0200
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
001B16
Chip select expansion register
Note :Set CSEiW bits (i = 0 to 3) after setting the corresponding CSiW bit (i = 0 to 3) of the CSR register
to "0". When CSiW bits are set to "1", CSEiW bits must be returned to "002".
When reset
0016
Bit Name
CSE0W
CSE1W
CSE2W
CSE3W
CS0wait expansion bit
CS1wait expansion bit
CS2wait expansion bit
CS3wait expansion bit
0 0 : 1 Wait state
0 1 : 2 Wait states
1 0 : 3 Wait states
1 1 : Inhibited
O
b7
b0
b6
b5
b4
b3
b2
b1
O
Bit Symbol
Function
R
W
Symbol
CSR
Address
000816
Chip select control register
When reset
0116
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
CS0wait bit
CS1wait bit
CS2wait bit
CS3wait 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