7733 datasheet(692/940 Pages) RENESAS

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CONNECTING EXTERNAL DEVICES

7735 Group User’s Manual

12–16

12.2 Software wait

The software wait facilitates access to external devices which require a long access time. There are two

types of software waits: wait 0 and wait 1.

The software wait is set by the wait bit (bit 2 at address 5E16) and the wait selection bit (bit 0 at address

5F16). (Refer to Table 12.2.1.) Figure 12.2.1 shows the structures of the processor mode register 0 (address

5E16) and processor mode register 1 (address 5F16). Figure 12.2.2 shows bus timing examples when the

software wait is used.

The software wait is valid only for the external area. (Access to the internal areas is always performed with

no wait.)

For external devices which can not be accessed even when using the software wait, by using the ready

_____

function (signal RSMP), a wait which is equivalent to 1 cycle of clock

φ1 can furthermore be generated.

(Refer to section “12.3 Ready function.”

Table 12.2.1 Setting method of software wait

Wait bit

Wait selection bit

Software wait

Bus cycle

Invalid (No wait)

Wait 0

Wait 1

Cycle of “internal clock

φ divided by 2”

(clock

φ1’s cycle ! 2)

“Cycle in the no-wait state” ! 2

(clock

φ1’s cycle ! 4 )

“Cycle in the no-wait state” ! 1.5

(clock

φ1’s cycle ! 3 )

12.2 Software wait

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