CC2430
8051 CPU : CPU Registers
11.3.3
Program Status Word
The Program Status Word (PSW) contains
several bits that show the current state of the
CPU. The Program Status Word is accessible
as an SFR and it is bit-addressable. PSW is
shown below and contains the Carry flag,
Auxiliary Carry flag for BCD operations,
Register Select bits, Overflow flag and Parity
flag. Two bits in PSWare uncommitted and can
be used as user-defined status flags.
PSW (0xD0) – Program Status Word
Bit
Name
Reset
R/W
Description
7
0
R/W
Carry flag. Set to 1 when the last arithmetic operation
resulted in a carry (during addition) or borrow (during
subtraction), otherwise cleared to 0 by all arithmetic
operations.
CY
6
0
R/W
Auxiliary carry flag for BCD operations. Set to 1 when the
last arithmetic operation resulted in a carry into (during
addition) or borrow from (during subtraction) the high order
nibble, otherwise cleared to 0 by all arithmetic operations.
AC
5
0
R/W
R/W
User-defined, bit-addressable
F0
4:3
00
Register bank select bits. Selects which set of R7-R0
registers to use from four possible register banks in DATA
space.
RS[1:0]
00
01
10
11
Register Bank 0, 0x00 – 0x07
Register Bank 1, 0x08 – 0x0F
Register Bank 2, 0x10 – 0x17
Register Bank 3, 0x18 – 0x1F
2
0
R/W
Overflow flag, set by arithmetic operations. Set to 1 when
the last arithmetic operation resulted in a carry (addition),
borrow (subtraction), or overflow (multiply or divide).
Otherwise, the bit is cleared to 0 by all arithmetic
operations.
OV
1
0
0
0
R/W
R/W
User-defined, bit-addressable
F1
P
Parity flag, parity of accumulator set by hardware to 1 if it
contains an odd number of 1’s, otherwise it is cleared to 0
11.3.4
Accumulator
ACC is the accumulator. This is the source
and destination of most arithmetic instructions,
data transfers and other instructions. The
mnemonic for the accumulator (in instructions
involving the accumulator) refers to A instead
of ACC.
ACC (0xE0) – Accumulator
Bit
Name
Reset
R/W
Description
7:0
0x00
R/W
Accumulator
ACC[7:0]
11.3.5
B Register
The B register is used as the second 8-bit
argument during execution of multiply and
divide instructions. When not used for these
purposes it may be used as a scratch-pad
register to hold temporary data.
B (0xF0) – B Register
Bit
Name
Reset
R/W
Description
7:0
0x00
R/W
B register. Used in MUL/DIV instructions.
B[7:0]
CC2430 Data Sheet (rev. 2.1) SWRS036F
Page 43 of 211
TAOS [ TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS ]
