HD6432142 datasheet(215/1177 Pages) RENESAS

215 / 1177 page

Section 6 Bus Controller

Rev. 4.00 Sep 27, 2006 page 171 of 1130

REJ09B0327-0400

6.4.5

Wait Control

When accessing external space, the MCU can extend the bus cycle by inserting one or more wait

states (T

W). There are three ways of inserting wait states: program wait insertion, pin wait insertion

using the

WAIT pin, and a combination of the two.

Program Wait Mode: In program wait mode, the number of T

W states specified by bits WC1 and

WC0 are always inserted between the T

2 and T3 states when external space is accessed.

Pin Wait Mode: In pin wait mode, the number of T

W states specified by bits WC1 and WC0 are

always inserted between the T

2 and T3 states when external space is accessed. If the WAIT pin is

low at the fall of

φ in the last T

2 or TW state, another TW state is inserted. If the WAIT pin is held

low, T

W states are inserted until it goes high.

Pin wait mode is useful for inserting four or more wait states, or for changing the number of T

states for different external devices.

Pin Auto-Wait Mode: In pin auto-wait mode, if the

WAIT pin is low at the fall of φ in the T

state, the number of T

W states specified by bits WC1 and WC0 are inserted when external space is

accessed. No additional T

W states are inserted even if the WAIT pin remains low. Pin auto-wait

mode can be used for an easy interface to low-speed memory, simply by routing the chip select

signal to the

WAIT pin.

Figure 6.13 shows an example of wait state insertion timing.

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