h8s-2172 Renesas Electronics Corporation., h8s-2172 Datasheet - Page 175

• Manufacturer Part Number: h8s-2172
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family H8s-2100 Series
• Manufacturer: Renesas Electronics Corporation.

Consecutive Reads in Different Areas: If consecutive reads in different areas occur while the
IDLE1 and IDLE0 bits in BCR are set to either B'01, B'10, or B'11, an idle cycle which is set by
the IDLC1 and IDLC0 bits in BCR is inserted at the start of the second read cycle.
Figure 6.44 shows an example of the operation in this case. In this example, bus cycle A is a read
cycle for ROM with a long output floating time, and bus cycle B is a read cycle for SRAM, each
being located in a different area. In (a), an idle cycle is not inserted, and a collision occurs in bus
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.
Write after Read: If an external write occurs after an external read while the IDLE1 and IDLE0
bits in BCR are set to either B'10 or B'11, an idle cycle which is set by the IDLC1 and IDLC0 bits
in BCR is inserted at the start of the write cycle.
Figure 6.45 shows an example of the operation in this case. In this example, bus cycle A is a read
cycle for ROM with a long output floating time, and bus cycle B is a CPU write cycle. In (a), an
idle cycle is not inserted, and a collision occurs in bus cycle B between the read data from ROM
and the CPU write data. In (b), an idle cycle is inserted, and a data collision is prevented.
Address bus
(area A)
(area B)
Data bus
φ
T
(a) No idle cycle insertion
1
Bus cycle A
Long output floating time
(IDLE1 = 0, IDLE0 = 0)
T
2
Figure 6.44 Example of Idle Cycle Operation
y
(Consecutive Reads in Different Areas)
T
3
Bus cycle B
T
1
T
2
Data collision
Address bus
Data bus
(area A)
(area B)
φ
(b) Idle cycle insertion
T
Rev. 2.00, 03/04, page 143 of 534
1
Bus cycle A
(IDLE1 = 0, IDLE0 = 0, IDLC1 = 0,
IDLC0 = 0)
T
2
T
3
Idle cycle
T
Bus cycle B
i
T
1
T
2