
CHAPTER 5 BUS CONTROL FUNCTION
User
’
s Manual U15862EJ3V0UD
270
5.5 Bus Access
5.5.1 Number of clocks for access
The following table shows the number of basic clocks required for accessing each resource.
Area (Bus Width)
Bus Cycle Type
Internal ROM (32 Bits)
Internal RAM (32 Bits)
External Memory (16 Bits)
Instruction fetch (normal access)
1
1 or 2
3 + n
Note
Instruction fetch (branch)
2
1 or 2
3+ n
Note
Operand data access
3
1
3 +n
Note
Note
2 + n clocks (n: Number of wait states) when the separate bus mode is selected (V850ES/KG1 and V850ES/KJ1).
Remark
Unit: Clocks/access
5.5.2 Bus size setting function
The bus size of each external memory area selected by CSn can be set (to 8 bits or 16 bits) by using the BSC
register.
The external memory area of the V850ES/KJ1 (0100000H to 0FFFFFFH) is selected by CS0 to CS3.
The external memory area of the V850ES/KG1 (0100000H to 03FFFFFH) is selected by CS0 and CS1.
The external memory area of the V850ES/KF1 (0100000H to 010FFFFH and 0200000H to 020FFFFH) is selected
by CS0 and CS1.
(1) Bus size configuration register (BSC)
This register can be read or written in 16-bit units.
Caution
Write to the BSC register 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 settings of the BSC register are complete. However, external memory areas whose
initial settings are complete may be accessed.
After reset: 5555H R/W Address: FFFFF066H
0
0
BSn0
0
1
8 bits
16 bits
BSC
1
BS30
Note
0
0
1
BS20
Note
0
0
1
BS10
0
0
1
BS00
8
9
10
11
12
13
Data bus width of CSn space (n = 0 to 3)
14
15
1
2
3
4
5
6
7
0
CS0
CS3
CSn signal
CS2
CS1
Note
The BS30 and BS20 bits are only valid in the V850ES/KJ1. Changing
these bits has no effect on the operation in the V850ES/KF1 and
V850ES/KG1.
Caution
Be sure to set bits 14, 12, 10, and 8 to 1, and clear bits 15, 13,
11, 9, 7, 5, 3, and 1 to 0.