CHAPTER 4 BUS CONTROL FUNCTION
104
User’s Manual U14359EJ4V0UM
4.5.2 Bus sizing function
The bus sizing function controls the data bus width for each CS space. The data bus width is specified by using
the bus size configuration register (BSC).
(1) Bus size configuration register (BSC)
This register can be read/written in 16-bit units.
Be sure to set bits 15, 13, 11, 9, 7, 5, 3, and 1 to 0. If they are set to 1, the operation is not guaranteed.
Cautions 1. Write to the BSC register after reset, and then do not change the set value. Also, do not
access an external memory area other than the one for this initialization routine until the
initial setting of the BSC register is complete. However, it is possible to access external
memory areas whose initialization settings are complete.
2. When the data bus width is specified as 8 bits, only the signals shown below become
active.
LWR:
When accessing SRAM, external ROM, or external I/O (write cycle)
LCAS: When accessing EDO DRAM
15
0
BSC
CSn signal
Address
FFFFF066H
After reset
Note
0000H/5555H
14
BS70
13
0
12
BS60
11
0
10
BS50
9
0
8
BS40
7
0
6
BS30
5
0
4
BS20
3
0
2
BS10
1
0
0
BS00
CS3
CS2
CS1
CS0
CS4
CS5
CS6
CS7
Note
When in single-chip mode 0, 1: 5555H
When in ROMless mode 0:
5555H
When in ROMless mode 1:
0000H
Bit position
Bit name
Function
Data Bus Width
Sets the data bus width of the CSn space.
BSn0
Data bus width of CSn space
0
8 bits
1
16 bits
14, 12, 10, 8,
6, 4, 2, 0
BSn0
(n = 0 to 7)
Содержание V850E/MA1
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