SN8P1600
8-bit micro-controller
WORKING REGISTERS
The RAM bank0 locations 82H to 84H store the specially defined registers such as register R, Y, Z, respectively shown
in the following table. These registers can use as the general-purpose working buffer or access ROM’s and RAM’s
data. For instance, all of the ROM table can be looked-up by R, Y and Z registers. The data of RAM memory can be
indirectly accessed with Y and Z registers.
Y, Z REGISTERS
The Y and Z registers are the 8-bit buffers. There are three major functions of these registers. First, Y and Z registers
can be used as working registers. Second, these two registers can be used as data pointers for @YZ register. Third,
the registers can address ROM location to look up ROM data.
084H
Y
Read/Write
After reset
Bit 7
YBIT7
R/W
0
Bit 6
YBIT6
R/W
0
Bit 5
YBIT5
R/W
0
Bit 4
YBIT4
R/W
0
Bit 3
YBIT3
R/W
0
Bit 2
YBIT2
R/W
0
Bit 1
YBIT1
R/W
0
Bit 0
YBIT0
R/W
0
083H
Z
Read/Write
After reset
Bit 7
ZBIT7
R/W
0
Bit 6
ZBIT6
R/W
0
Bit 5
ZBIT5
R/W
0
Bit 4
ZBIT4
R/W
0
Bit 3
ZBIT3
R/W
0
Bit 2
ZBIT2
R/W
0
Bit 1
ZBIT1
R/W
0
Bit 0
ZBIT0
R/W
0
The @YZ that is data point_1 index buffer located at address 0E7H in RAM bank 0. It employs Y and Z registers to
addressing RAM location to read/write data through ACC. The Lower 4-bit of Y register points to RAM bank number
and Z register to RAM address number, respectively. The higher 4-bit data of Y register is truncated in RAM indirectly
access mode.
ꢃ
Example: Following example uses indirectly addressing mode to access data in the RAM address 025H of
bank0.
B0MOV
B0MOV
B0MOV
Y, #00H
Z, #25H
A, @YZ
; To set RAM bank 0 for Y register
; To set location 25H for Z register
; To read a data into ACC
ꢃ
Example: Clear general-purpose data memory area of bank 0 using @YZ register.
B0MOV
B0MOV
Y, #0
Z, #07FH
; Y = 0, bank 0
; Z = 7FH, the last address of the data memory area
CLR_YZ_BUF:
CLR
@YZ
; Clear @YZ to be zero
DECMS
JMP
Z
; Z – 1, if Z= 0, finish the routine
; Not zero
CLR_YZ_BUF
CLR
.
@YZ
END_CLR:
; End of clear general purpose data memory area of bank 0
ꢂ
Note: Please consult the “LOOK-UP TABLE DESCRIPTION” about Y, Z register look-up table application.
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