Datasheet

Section 6 Bus Controller
Page 140 of 846 REJ09B0140-0900 Rev. 9.00
Sep 16, 2010
H8S/2215 Group
6.7.1 Basic Timing
The number of states in the initial cycle (full access) of the burst ROM interface is in accordance
with the setting of the AST0 bit in ASTCR. Also, when the AST0 bit is set to 1, wait state
insertion is possible. One or two states can be selected for the burst cycle, according to the setting
of the BRSTS1 bit in BCRH. Wait states cannot be inserted. When area 0 is designated as burst
ROM space, it becomes 16-bit access space regardless of the setting of the ABW0 bit in ABWCR.
When the BRSTS0 bit in BCRH is cleared to 0, burst access of up to 4 words is performed; when
the BRSTS0 bit is set to 1, burst access of up to 8 words is performed.
The basic access timing for burst ROM space is shown in figures 6.20 and 6.21. The timing shown
in figure 6.20 is for the case where the AST0 and BRSTS1 bits are both set to 1, and that in figure
6.21 is for the case where both these bits are cleared to 0.
T
1
Address bus
φ
CS0
AS
Data bus
T
2
T
3
T
1
T
2
T
1
Full access
T
2
RD
Burst access
Only lower address changed
Read data Read data Read data
Figure 6.20 Example of Burst ROM Access Timing (When AST0 = BRSTS1 = 1)