134
Chapter 4
Bus Control Function
Preliminary User’s Manual U15839EE1V0UM00
4.9 Idle State Insertion Function
To facilitate interfacing with low-speed memory devices, an idle state (TI) can be inserted into the cur-
rent bus cycle after the T2 state to meet the data output float delay time (tdf) on memory read access
for each CS space. The bus cycle following the T2 state starts after the idle state is inserted.
An idle state is inserted after read/write cycles for SRAM, external I/O, or external ROM.
In the following cases, an idle state is inserted in the timing.
• after read/write cycles for SRAM, external I/O, or external ROM
The idle state insertion setting can be specified by program using the bus cycle control register (BCC).
Immediately after the system reset, idle state insertion is automatically programmed for all memory
blocks.
(1)
Bus cycle control register (BCC)
This register can be read/written in 16-bit units.
Cautions: 1. The internal iCache area, the internal RAM area and the 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 that for this initialization rou-
tine until initial setting of the BCC register is finished. However, it is possible to
access external memory areas whose initialization has been finished.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Address
Initial
value
BCC BC71 BC70 BC61 BC60 BC51 BC50 BC41 BC40 BC31 BC30 BC21 BC20 BC11 BC10 BC01 BC00 FFFFF488H FFFFH
CS7
CS6
CS5
CS4
CS3
CS2
CS1
CS0
Bit Position
Bit Name
Function
15 to 0
BCn1,
BCn0
(n = 0 to 7)
Data Cycle
Specifies the insertion of an idle state when accessing corresponding CSn area.
BCn1
BCn0
Idle State in CSn Area
0
0
Not inserted
0
1
1
1
0
2
1
1
3
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