CHAPTER 4 BUS CONTROL FUNCTION
User’s Manual U12688EJ4V0UM00
107
4.5
Bus Access
4.5.1 Number of access clocks
The number of basic clocks necessary for accessing each resource is as follows.
Instruction Fetch
Operand Data Access
Bus Cycle Configuration
Resource (Bus Width)
Normal
Access
Burst Access
Normal
Access
Burst
Access
Internal ROM (32 bits)
1
3
Internal RAM (32 bits)
1 or 2
1
Internal peripheral I/O (16 bits)
3 + n
SRAM, external ROM, external I/O (16/8 bits)
2 + n
2 + n
During DMA flyby transfer
2 + n
Page ROM (16/8 bits)
2 + n
2 + n
2 + n
2 + n
High-speed page DRAM (16/8 bits)
3 + n
2 + n
3 + n
2 + n
During read
3 + n
2 + n
During DMA flyby
transfer
During write
3 + n
3 + n
EDO DRAM (16/8 bits)
3 + n
1 + n
3 + n
1 + n
During read
3 + n
2 + n
External
device
During DMA flyby
transfer
During write
3 + n
3 + n
Remarks 1. Unit: Clock/access
2. n:
Number of wait insertions
(1) Internal peripheral I/O interface
The contents of the access to internal peripheral I/O are not output to the external bus. Therefore, during
instruction fetch access, internal peripheral I/O access can be performed in parallel.
Internal peripheral I/O access is basically 3-clock access. However, on some occasions, access to internal
peripheral I/O registers with timer/counter functions also involves a wait.
I
nternal Peripheral I/O Register
Access
Waits
Clock Cycles
Read
1
4
CC1n0 to CC1n3,
TM1n (n = 0 to 5)
Write
0/1
3/4
Read
0
3
CM40, CM41
Write
0/1
3/4
Read
0/1
3/4
TM40, TM41
Write
0
3
Read
0
3
Other
Write
0
3
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