
7902 Group User's Manual
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
register specify the direct page area in bank 016 or in the space across banks 016 and 116. The following
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 select
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 select bit
0
DPR0
256 bytes
1
DPR0toDPR3
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
g 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 select 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 select 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