p2125vps20 Renesas Electronics Corporation., p2125vps20 Datasheet - Page 159

• Manufacturer Part Number: p2125vps20
• Description: 16-bit Single-chip Microcomputer H8s Family / H8s/2100 Series
• Manufacturer: Renesas Electronics Corporation.

6.6.2
As with the basic bus interface, program wait insertion or pin wait insertion using the WAIT pin
can be used in the initial cycle (full access) of the burst ROM interface. For details, see section
6.5.4, Wait Control. Wait states cannot be inserted in a burst cycle.
6.7
When this LSI accesses the external address space, it can insert a 1-state idle cycle (T
bus cycles 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 and I/O interfaces.
If an external write occurs after an external read while the ICIS0 bit is set to 1 in BCR, an idle
cycle is inserted at the start of the write cycle.
Figure 6.10 shows examples of idle cycle operation. In these examples, 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 figure 6.10 (a),
with no idle cycle inserted, a collision occurs in bus cycle B between the read data from ROM and
the CPU write data. In figure 6.10 (b), an idle cycle is inserted, thus preventing data collision.
Figure 6.9 Access Timing Example in Burst ROM Space (AST = BRSTS1 = 0)
Wait Control
Idle Cycle
Address bus
(IOSE = 0)
Data bus
AS/IOS
RD
φ
T
1
Full access
Read data
T
2
Only lower
Read data Read data
T
Burst access
1
address changes
Rev. 1.00 Sep. 21, 2006 Page 121 of 658
T
1
Section 6 Bus Controller (BSC)
REJ09B0310-0100
I
) between