H8S2245 datasheet(214/818 Pages) RENESAS

214 / 818 page

Section 6 Bus Controller

Rev.3.00 Mar. 26, 2007 Page 172 of 772

REJ09B0355-0300

6.7.2

Pin States in Idle Cycle

Table 6.5 shows pin states in an idle cycle.

Table 6.5

Pin States in Idle Cycle

Pins

Pin State

23 to A0

Contents of next bus cycle

15 to D0

High impedance

CSn

High

HWR

High

LWR

High

6.8

Bus Release

6.8.1

Overview

The H8S/2245 Group can release the external bus in response to a bus request from an external

device. In the external bus released state, the internal bus master continues to operate as long as

there is no external access.

If an internal bus master wants to make an external access in the external bus released state, it can

issue a bus request off-chip.

6.8.2

Operation

In external expansion mode, the bus can be released to an external device by setting the BRLE bit

in BCRL to 1. Driving the

BREQ pin low issues an external bus request to the H8S/2245 Group.

When the

BREQ pin is sampled, at the prescribed timing the BACK pin is driven low, and the

address bus, data bus, and bus control signals are placed in the high-impedance state, establishing

the external bus-released state.

In the external bus released state, an internal bus master can perform accesses using the internal

bus. When an internal bus master wants to make an external access, it temporarily defers

activation of the bus cycle, and waits for the bus request from the external bus master to be

dropped.

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