HD64F2149YV datasheet(189/1075 Pages) RENESAS

189 / 1075 page

Section 6 Bus Controller

Rev. 3.00 Jan 18, 2006 page 161 of 1044

REJ09B0280-0300

6.5

Burst ROM Interface

6.5.1

Overview

With the H8S/2169 or H8S/2149, external space area 0 can be designated as burst ROM space,

and burst ROM interfacing can be performed.

External space can be designated as burst ROM space by means of the BRSTRM bit in BCR.

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.

6.5.2

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 AST bit. Also, when the AST 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

BCR. Wait states cannot be inserted.

When the BRSTS0 bit in BCR 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 6.14 (a) and (b). The timing

shown in figure 6.14 (a) is for the case where the AST and BRSTS1 bits are both set to 1, and that

in figure 6.14 (b) is for the case where both these bits are cleared to 0.

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