71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
Accumulator (ACC, A): ACC is the accumulator register. Most instructions use the accumulator to hold the operand. The
mnemonics for accumulator-specific instructions refer to accumulator as “A”, not ACC.
B Register: The B register is used during multiply and divide instructions. It can also be used as a scratch-pad register to hold
temporary data.
Program Status Word (PSW):
MSB
CV
LSB
AC
F0
RS1
RS
OV
-
P
Table 8: PSW Register Flags
Bit
Symbol
Function
Carry flag
PSW.7
PSW.6
PSW.5
CV
AC
F0
Auxiliary Carry flag for BCD operations
General purpose Flag 0 available for user.
F0 is not to be confused with the F0 flag in the CE STATUS register.
PSW.4
PSW.3
RS1
RS0
Register bank select control bits. The contents of RS1 and RS0 select the working
register bank:
RS1/RS0
00
Bank selected
Bank 0
Location
(0x00 – 0x07)
(0x08 – 0x0F)
(0x10 – 0x17)
(0x18 – 0x1F)
01
Bank 1
10
Bank 2
11
Bank 3
PSW.2
PSW.1
PSW.0
OV
-
Overflow flag
User defined flag
P
Parity flag, affected by hardware to indicate odd / even number of “one” bits in the
Accumulator, i.e. even parity.
Table 9: PSW Bit Functions
Stack Pointer (SP): The stack pointer is a 1-byte register initialized to 0x07 after reset. This register is incremented before
PUSH and CALL instructions, causing the stack to begin at location 0x08.
Data Pointer: The data pointer (DPTR) is 2 bytes wide. The lower part is DPL, and the highest is DPH. It can be loaded as two
registers (e.g. MOV DPL,#data8). It is generally used to access external code or data space (e.g. MOVC A,@A+DPTR or
MOVX A,@DPTR respectively).
Program Counter: The program counter (PC) is 2 bytes wide initialized to 0x0000 after reset. This register is incremented
when fetching operation code or when operating on data from program memory.
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