7905 datasheet(29/565 Pages) RENESAS

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7905 Group User’s Manual Rev.1.0

CENTRAL PROCESSING UNIT (CPU)

2.1 Central processing unit (CPU)

2-6

2.1.8 Direct page register 0 to 3 (DPR0 to DPR3)

Each of direct page registers 0 to 3 (hereafter called the “DPRi”) is a 16-bit register. The contents of this

addressing modes use DPRi.

The contents of the DPRi indicate the base address (the lowest address) of the direct page area. The direct

page area is specified in the space above this address.

After reset, whether to use DPR0 only or DPR0 to DPR3 can be selected by the direct page register switch

bit. (See Figure 2.1.5). This selection specifies the direct page area. Table 2.1.1 lists the selection of the

direct page register. Figure 2.1.4 shows setting examples of the direct page area.

At reset, DPR0 = “000016,” and each of DPR1 to DPR3 becomes undefined.

q Addressing modes using direct page register

Table 2.1.1 Selection of direct page register

Usable DPRi

Direct page area

Direct page register switch bit

DPR0

256 bytes

DPR0 to DPR3

64 bytes at

each DPRi

Fig. 2.1.4 Setting examples of direct page area

• Direct

• Direct indexed X

• Direct indexed Y

• Direct indirect

• Direct indexed X indirect

• Direct indirect indexed Y

• Direct indirect long

• Direct indirect long indexed Y

• Direct bit relative

❈ Refer to “7900 Series Software Manual” for addressing modes and instructions.

1000F16

1000016

1000F16

Bank 016

016

FF16

12316

22216

FF1016

1000016

FFFF16

When DPR0 = 000016

When DPR0 = 012316

When DPR0 = FF1016

Note: When the low-order 8 bits of DPRi = “00,” the number of cycles required for address generation becomes 1 cycle smaller.

The direct page area is specified in space across banks 016

and 116 when DPR0 is “FF0116” or more.

s Direct page register switch bit = 0

016

3F16

4016

7F16

FFD016

FFFF16

Bank 016

When DPR0 = 000016

When DPR1 = 004016

When DPR3 = FFD016

80016

83F16

When DPR2 = 080016

s Direct page register switch bit = 1

016

The direct page area is specified in the space across banks 016

and 116 when DPRi is “FFC116” or more.

Bank 116

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