SN8F2250B Series
USB 2.0 Full-Speed 8-Bit Micro-Controller
2.1.4.7 Y, Z REGISTERS
The Y and Z registers are the 8-bit buffers. There are three major functions of these registers.
z
z
z
can be used as general working registers
can be used as RAM data pointers with @YZ register
can be used as ROM data pointer with the MOVC instruction for look-up table
084H
Y
Read/Write
After reset
Bit 7
YBIT7
R/W
-
Bit 6
YBIT6
R/W
-
Bit 5
YBIT5
R/W
-
Bit 4
YBIT4
R/W
-
Bit 3
YBIT3
R/W
-
Bit 2
YBIT2
R/W
-
Bit 1
YBIT1
R/W
-
Bit 0
YBIT0
R/W
-
083H
Z
Read/Write
After reset
Bit 7
ZBIT7
R/W
-
Bit 6
ZBIT6
R/W
-
Bit 5
ZBIT5
R/W
-
Bit 4
ZBIT4
R/W
-
Bit 3
ZBIT3
R/W
-
Bit 2
ZBIT2
R/W
-
Bit 1
ZBIT1
R/W
-
Bit 0
ZBIT0
R/W
-
Example: Uses Y, Z register as the data pointer 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
Example: Uses the Y, Z register as data pointer to clear the RAM data.
B0MOV
B0MOV
Y, #0
Z, #07FH
; Y = 0, bank 0
; Z = 7FH, the last address of the data memory area
CLR_YZ_BUF:
END_CLR:
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 of clear general purpose data memory area of bank 0
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