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CONNECTION WITH EXTERNAL DEVICES

3.2 Software Wait

7721 Group User's Manual

3–8

3.2 Software Wait

Software Wait provides a function to facilitate access to external devices that require long access time. To

select the software Wait, use the wait bit (bit 2 at address 5E16). Figure 3.2.1 shows the structure of

processor mode register 0 (address 5E16). Figure 3.2.2 shows examples of bus timing when software Wait

is used.

Software Wait is valid only for the eternal area. The internal area is always accessed with no Wait.

Fig. 3.2.1 Structure of processor mode register 0

Bit

Bit name

Functions

At reset

Fix this bit to “0.”

Software reset bit

Interrupt priority detection time

select bits

Stack bank select bit

The microcomputer is reset by

writing “1” to this bit. The value is

“0” at reading.

0 0 : 7 cycles of

0 1 : 4 cycles of

1 0 : 2 cycles of

1 1 : Do not select.

0 : Bank 016

1 : Bank FF16

b5 b4

Processor mode register 0 (Address 5E16)

–

Fix this bit to “0.”

Nothing is assigned.

The value is “1” at reading.

Wait bit

0 : Software Wait is inserted when

accessing external area.

1 : No software Wait is inserted

when accessing external area.

: Bits 0, 1, and 3 to 6 are not used for accessing external area.

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