deveopmen
Rev.B2 for proof reading
Bus Control
Mitsubishi Microcomputers
M32C/83 group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
56
Example 1:
After accessing the external area, the
address bus and chip select signal both are
changed in the next cycle.
The following example shows the other chip select
signal accessing area (j) in the cycle after having
accessed external area (i). In this case, the address
bus and chip select signal both change between the
two cycles.
Access to
external
area (i)
Note: These examples show the address bus and chip select signal for two consecutive cycles.
By combining these examples, chip select signal can be extended beyond two cycles.
Data bus
Address bus
Chip select
(CSi)
Chip select
(CSj)
Access to
external
area (j)
Address
Data
Data
Example 2:
After accessing the external area, only the
chip select signal is changed in the next
cycle. (The address bus does not change.)
The following example shows the CPU accesses the
internal ROM/RAM area in the cycle after having
accessed external area. In this case, the chip select
signal changes between the two cycles but the
address bus does not.
Example 3:
After accessing the external area, only the
address bus is changed in the next cycle.
(The chip select signal does not change.)
The following example shows the same chip select
signal accessing area (i) in the cycle after having
accessed external area (i). In this case, the address
bus changes between the two cycles, but the chip
select signal does not.
Data bus
Address bus
Chip select
(CSi)
Data
Address
Data bus
Address bus
Chip select
Data
Address
Access to
external
area
No access
Access to
external
area (i)
Access to
external
area (i)
Data bus
Address bus
Chip select
Data
Address
Example 4:
After accessing the external area, the
address bus and chip select signal both are
not changed in the next cycle.
The following example shows CPU does not access
any area in the cycle after having accessed external
area (no instruction pre-fetch is occurred). In this
case, the address bus and the chip select signal do
not change between the two cycles.
Data
Access to
external
area
Access to
internal
ROM/RAM
area
The chip select signal turns Low (active) in synchronize with the address bus. However, its turning High
depends on the area accessed in the next cycle. Figure 1.7.2 shows the output examples of the address
bus and chip select signals.
Figure 1.7.2. Example of address bus and chip select signal outputs (Separate bus)