HD6412320 RENESAS [Renesas Technology Corp], HD6412320 Datasheet - Page 233

• Manufacturer Part Number: HD6412320
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family H8S-2300 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

6.8
6.8.1
When the chip accesses external space, it can insert a 1-state idle cycle (T
the following two cases: (1) when read accesses in different areas occur consecutively, and (2)
when a write cycle occurs immediately after a read cycle. By inserting an idle cycle it is possible,
for example, to avoid data collisions between ROM, with a long output floating time, and high-
speed memory, I/O interfaces, and so on.
Consecutive Reads in Different Areas: If consecutive reads in different areas occur while the
ICIS1 bit in BCRH is set to 1, an idle cycle is inserted at the start of the second read cycle. This is
enabled in advanced mode.
Figure 6.31 shows an example of the operation in this case. In this example, bus cycle A is a read
cycle from ROM with a long output floating time, and bus cycle B is a read cycle from SRAM,
each being located in a different area. In (a), an idle cycle is not inserted, and a collision occurs in
cycle B between the read data from ROM and that from SRAM. In (b), an idle cycle is inserted,
and a data collision is prevented.
Address bus
CS (area A)
CS (area B)
Data bus
RD
Idle Cycle
Operation
φ
(a) Idle cycle not inserted
T
1
Bus cycle A
(ICIS1 = 0)
T
Figure 6.31 Example of Idle Cycle Operation (1)
2
T
Long output
floating time
3
Bus cycle B
T
1
T
2
Data
collision
Address bus
CS (area A)
CS (area B)
Data bus
Rev.6.00 Sep. 27, 2007 Page 203 of 1268
RD
φ
T
1
(b) Idle cycle inserted
Bus cycle A
(ICIS1 = 1 (initial value))
T
2
Section 6 Bus Controller
I
) between bus cycles in
T
3
REJ09B0220-0600
T
Bus cycle B
I
T
1
T
2