M16C80 Datasheet, PDF (44/358 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/80 SERIES

M16C/80 Group
7. Bus
7.2 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.
(1) Address bus/data bus
____
____
There are 24 pins, A0 to A22 and A23 for the address bus for accessing the 16 Mbytes address space. A23
is an inverted output of the MSB of the address.
The data bus consists of pins for data IO. The external data bus control register (address 000B16) selects
the 8-bit data bus, D0 to D7 for each external area, or the 16-bit data bus, D0 to D15. After a reset, there is
by default an 8-bit data bus for the external area 3 when the BYTE pin is “H”, or a 16-bit data bus when the
BYTE pin is “L”.
When shifting from single-chip mode to extended memory mode, the value on the address bus is unde-
fined until an external area is accessed.
When accessing a DRAM area with DRAM control in use, a multiplexed signal consisting of row address
and column address is output to A8 to A20.
(2) Chip select signals
____
The chip select signals share A0 to A22 and A23. You can use bits 0 and 1 of the processor mode register
1 (address 000516) to set the external area mode, then select the chip select area and number of address
outputs.
In microprocessor mode, external area mode 0 is selected after a reset. The external area can be split
into a maximum of four using the chip select signals. Table 7.4 shows the external areas specified by the
chip select signals.
Table 7.4 External areas specified by the chip select signals
Memory space
expansion
mode
Processor mode
Chip select signal
CS0
CS1
CS2
Mode 0
(A23)
(A22)
(A21)
Memory expansion mode
Mode 1
Microprocessor mode
C0000016 to
DFFFFF16
(2 Mbytes)
E0000016 to
FFFFFF16
(2 Mbytes)
00800016 to
1FFFFF16
(2016 Kbytes)
20000016 to
3FFFFF16
(2 Mbytes)
Memory expansion mode
Mode 2
Microprocessor mode
Memory expansion mode
Mode 3
Microprocessor mode
C0000016 to
EFFFFF16
(3 Mbytes)
C0000016 to
FFFFFF16
(4 Mbytes)
E0000016 to
EFFFFF16
(1 Mbytes)
F0000016 to
FFFFFF16
(1 Mbytes)
00800016 to
3FFFFF16
(4064 Kbytes)
10000016 to
1FFFFF16
(1 Mbytes)
(A21)
20000016 to
2FFFFF16
(1 Mbytes)
CS3
(A20)
(A20)
(A20)
C0000016 to
CFFFFF16
(1 Mbytes)
Rev.1.00 Aug. 02, 2005 ^{Page 33} of 329
REJ09B0187-0100