CHAPTER 4 BUS CONTROL FUNCTION
User’s Manual U12688EJ4V0UM00
113
4.6 Wait Function
4.6.1 Programmable wait function
With the aim of realizing easy interfacing with low-speed memory or with I/Os, it is possible to insert up to 7 data
wait states with respect to the starting bus cycle for each memory block.
The number of wait states can be set by data wait control registers 1 and 2 (DWC1, DWC2) and can be specified
by program. Just after system reset, all blocks have 7 data wait states inserted.
(1) Data wait control registers 1, 2 (DWC1, DWC2)
It is possible to read/write the DWC1 register in 16-bit units and the DWC2 register in 8/1-bit units.
15
DW71
DWC1
Memory
block
Address
FFFFF060H
After reset
FFFFH
14
DW70
13
DW61
12
DW60
11
DW51
10
DW50
9
DW41
8
DW40
7
DW31
6
DW30
5
DW21
4
DW20
3
DW11
2
DW10
1
DW01
0
DW00
7
6
5
4
3
2
1
0
Memory
block
7
6
5
4
3
2
1
0
Address
FFFFF06AH
7
DW72
DWC2
6
DW62
5
DW52
4
DW42
3
DW32
2
DW22
1
DW12
0
DW02
After reset
FFH
Register
Name
Bit
Position
Bit Name
Function
Data Wait
Specifies the number of wait states inserted in memory block n.
Registers DWC1 and DWC2 are set in combination.
DWn2
DWn1
DWn0
Number of Wait States Inserted in
Memory Block n
DWC1
15 to 0
DWn1,
DWn0
(n = 7 to 0)
0
0
0
0
0
0
1
1
0
1
0
2
0
1
1
3
1
0
0
4
1
0
1
5
1
1
0
6
1
1
1
7
DWC2
7 to 0
DWn2
(n = 7 to 0)
Cautions 1. The internal ROM area and internal RAM area are not subject to programmable waits and
ordinarily no wait access is carried out. Neither is the internal peripheral I/O area subject
to programmable wait states, with wait control performed only by each peripheral function.
2. In the following cases, the settings of registers DWC1 and DWC2 are invalid (wait control
is performed by each memory controller).
•
DRAM access
•
Page ROM on-page access
3. Write to the DWC1 and DWC2 registers after reset, and then do not change the set values.
Also, do not access an external memory area other than the one for this initialization
routine until the initial setting of the DWC1 and DWC2 registers is complete. However, it is
possible to access an external memory area whose initialization is complete.
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