M30800MC Datasheet, PDF (28/317 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

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M16C/80
SINGLE-CHIP
Mitsubishi microcomputers
(100-pin version) group
16-BIT CMOS MICROCOMPUTER
Bus Settings
The BYTE pin, bit 0 to 3 of the external data bus width control register (address 000B16), bits 4 and 5 of the
processor mode register 0 (address 000416) and bit 0 and 1 of the processor mode register 1 (address
000516) are used to change the bus settings.
Table 1.7.1 shows the factors used to change the bus settings, figure 1.7.1 shows external data bus width
control register and table 1.7.2 shows external area 0 to 3 and external area mode.
Table 1.7.1. Factors for switching bus settings
Bus setting
Switching external address bus width
Switching external data bus width
Switching between separate and multiplex bus
Switching factor
External data bus width control register
BYTE pin (external area 3 only)
Bits 4 and 5 of processor mode register 0
(1) Selecting external address bus width
You can select the width of the address bus output externally from the 16 Mbytes address space, the
number of chip select signals, and the address area of the chip select signals. (Note, however, that when
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you select “Full CS space multiplex bus”, addresses A0 to A15 are output.) The combination of bits 0 and
1 of the processor mode register 1 allow you to set the external area mode.
When using DRAM controller, the DRAM area is output by multiplexing of the time splitting of the row and
column addresses.
(2) Selecting external data bus width
You can select 8-bit or 16-bit for the width of the external data bus for external areas 0, 1, 2, and 3. When
the data bus width bit of the external data bus width control register is “0”, the data bus width is 8 bits;
when “1”, it is 16 bits. The width can be set for each of the external areas. The default bus width for
external area 3 is 16 bits when the BYTE pin is “L” after a reset, or 8 bits when the BYTE pin is “H” after
a reset. The bus width selection is valid only for the external bus (the internal bus width is always 16 bits).
During operation, fix the level of the BYTE pin to “H” or “L”.
(3) Selecting separate/multiplex bus
The bus format can be set to multiplex or separate bus using bits 4 and 5 of the processor mode register 0.
• Separate bus
In this bus configuration, input and output is performed on separate data and address buses. The data
bus width can be set to 8 bits or 16 bits using the external data bus width control register. For all
programmable external areas, P0 is the data bus when the external data bus is set to 8 bits, and P1 is
a programmable IO port. When the external data bus width is set to 16 bits for any of the external
areas, P0 and P1 (although P1 is undefined for any 8-bit bus areas) are the data bus.
When accessing memory using the separate bus configuration, you can select a software wait using
the wait control register.
• Multiplex bus
In this bus configuration, data and addresses are input and output on a time-sharing basis. For areas
for which 8-bit has been selected using the external data bus width control register, the 8 bits D0 to D7
are multiplexed with the 8 bits A0 to A7. For areas for which 16-bit has been selected using the
external data bus width control register, the 16 bits D0 to D15 are multiplexed with the 16 bits A0 to
A15. When accessing memory using the multiplex bus configuration, two waits are inserted regard-
less of whether you select “No wait” or “1 wait’ in the appropriate bit of the wait control register.
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