HD6432621 Hitachi, HD6432621 Datasheet - Page 211

• Manufacturer Part Number: HD6432621
• Description: (HD64F262x Series) 16-Bit Microcomputer
• Manufacturer: Hitachi

7.5
7.5.1
With the H8S/2626 Series and H8S/2623 Series, external space area 0 can be designated as burst
ROM space, and burst ROM interfacing can be performed. The burst ROM space interface enables
16-bit configuration ROM with burst access capability to be accessed at high speed.
Area 0 can be designated as burst ROM space by means of the BRSTRM bit in BCRH.
Consecutive burst accesses of a maximum of 4 words or 8 words can be performed for CPU
instruction fetches only. One or two states can be selected for burst access.
7.5.2
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 7-14 (a) and (b). The timing
shown in figure 7-14 (a) is for the case where the AST0 and BRSTS1 bits are both set to 1, and
that in figure 7-14 (b) is for the case where both these bits are cleared to 0.
Burst ROM Interface
Overview
Basic Timing
167