7906 datasheet(41/531 Pages) RENESAS

41 / 531 page

7906 Group User’s Manual Rev.2.0

2-20

CENTRAL PROCESSING UNIT (CPU)

2.5 Processor modes

Fig. 2.5.3 Structure of processor mode register 0

2.5.2 Setting of processor mode

The processor mode is set by the following:

• Voltage level applied to the MD0 and MD1 pins

• Processor mode bits (bits 1 and 0 at address 5E16)

The VSS–level voltage must be applied to the MD0 and MD1 pins, because the M37906 operates only in

the single-chip mode. Also, the processor mode bit must be “00.”

Figure 2.5.2 shows the structure of the processor mode register 0 (address 5E16).

Bit name

Bit

Processor mode register 0 (Address 5E16)

Function

At reset

R/W

Processor mode bits

Interrupt priority detection time

select bits

Software reset bit

Fix this bit to “0.”

b7 b6 b5 b4 b3 b2 b1 b0

0 0 : Single-chip mode

0 1 : Do not select.

1 0 : Do not select.

1 1 : Do not select.

b1 b0

0 0 : 7 cycles of fsys

0 1 : 4 cycles of fsys

1 0 : 2 cycles of fsys

1 1 : Do not select.

b5 b4

The microcomputer is reset by writing “1” to this

bit. The value is “0” at reading.

0X X 0 0

Any of these bits may be either “0” or “1.”

X : It may be either “0” or “1.”

7906 Datasheet(PDF) 41 Page - Renesas Technology Corp