HD6432138SW datasheet(205/1061 Pages) RENESAS

205 / 1061 page

Section 6 Bus Controller

Rev. 4.00 Jun 06, 2006 page 151 of 1004

REJ09B0301-0400

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, 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 the system clock in the T

2 state, the

number of T

W states specified by bits WC1 and WC0 are inserted between the T2 and T3 states

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 6.7 shows an example of wait state insertion timing.

HD6432138SW Datasheet(PDF) 205 Page - Renesas Technology Corp