HD64F2145 datasheet(170/829 Pages) RENESAS

170 / 829 page

Rev. 2.0, 08/02, page 130 of 788

6.5.4

Wait Control

When accessing the external address space, this LSI 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

:$,7 pin, and the combination of program wait and the :$,7 pin.

Program Wait Mode: A specified number of wait states T

W can be inserted automatically

between the T

2 state and T3 state when accessing the external address space always according to

the settings of the WC1 and WC0 bits in WSCR.

Pin Wait Mode: A specified number of wait states T

W can be inserted automatically between the

2 state and T3 state when accessing the external address space always according to the settings of

the WC1 and WC0 bits. If the

:$,7 pin is low at the falling edge of ø in the last T

2 or TW state,

another T

W state is inserted. If the :$,7 pin is held low, TW states are inserted until it goes high.

This is useful when inserting four or more T

W states, or when changing the number of TW states to

be inserted for each external device.

Pin Auto-Wait Mode: A specified number of wait states T

W can be inserted automatically

between the T

2 state and T3 state when accessing the external address space according to the

settings of the WC1 and WC0 bits if the

:$,7 pin is low at the falling edge of ø in the last T

state. Even if the

:$,7 pin is held low, T

W states can be inserted only up to the specified number

of states.

This function enables the low-speed memory interface only by inputting the chip select signal to

the

:$,7 pin.

Figure 6.13 shows an example of wait state insertion timing in pin wait mode.

The settings after a reset are: 3-state access, 3 program wait insertion, and

:$,7 pin input

disabled.

HD64F2145 Datasheet(PDF) 170 Page - Renesas Technology Corp