CHAPTER 4 BUS CONTROL FUNCTION
User’s Manual U12688EJ4V0UM00
117
4.7
Idle State Insertion Function
To facilitate interfacing with low-speed memory devices, an idle state (TI) can be inserted into the current bus cycle
after the T2 state in order to meet the data output float delay time (t
DF
) on memory read accesses for each memory
block. The bus cycle following the T2 state starts after the idle state is inserted.
Specifying insertion of the idle state is programmable by setting the bus cycle control register (BCC).
Immediately after the system reset is cancelled, idle state insertion is automatically programmed for all memory
blocks.
The idle state is inserted only if the read cycle is followed by a write cycle.
(1) Bus cycle control register (BCC)
This register can be read/written in 16-bit units.
15
BC71
BCC
Address
FFFFF062H
After reset
5555H
14
BC70
13
BC61
12
BC60
11
BC51
10
BC50
9
BC41
8
BC40
7
BC31
6
BC30
5
BC21
4
BC20
3
BC11
2
BC10
1
BC01
0
BC00
Memory
block
7
6
5
4
3
2
1
0
Bit Position
Bit Name
Function
Bus Cycle
Specifies insertion of an idle state in memory block n.
BCn1
BCn0
Idle State in Memory Block n
0
0
Not inserted
0
1
Inserted
1
Optional
RFU (Reserved)
15 to 0
BCn1,
BCn0
(n = 7 to 0)
Cautions 1. The internal ROM area, internal RAM area and internal peripheral I/O area are not subject to
insertion of an idle state.
2. Write to the BCC 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 BCC register is complete. However, it is possible to access an
external memory area whose initialization is complete.
Содержание V850E/MS1 UPD703100
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