HD64F2149YV datasheet(187/1075 Pages) RENESAS

187 / 1075 page

Section 6 Bus Controller

Rev. 3.00 Jan 18, 2006 page 159 of 1044

REJ09B0280-0300

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, TW 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

2 state, the number of TW

states specified by bits WC1 and WC0 are inserted when external space is accessed. No additional

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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