73S1209F Data Sheet
DS_1209F_004
Program Status Word (PSW):
Table 9: PSW Register Flags
MSB LSB
CV AC F0 RS1 RS OV – P
Bit Symbol
Function
PSW.7 CV
Carry
flag.
PSW.6
AC
Auxiliary Carry flag for BCD operations.
PSW.5
F0
General purpose Flag 0 available for user.
PSW.4
RS1
Register bank select control bits. The contents of RS1 and RS0 select
the working register bank:
RS1/RS0 Bank
Selected
Location
00
Bank 0
(0x00 – 0x07)
01
Bank 1
(0x08 – 0x0F)
10
Bank 2
(0x10 – 0x17)
11
Bank 3
(0x18 – 0x1F)
PSW.3 RS0
PSW.2 OV
Overflow
flag.
PSW.1
F1
General purpose Flag 1 available for user.
PSW.0
P
Parity flag, affected by hardware to indicate odd / even number of “one”
bits in the Accumulator, i.e. even parity.
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 a 2-byte register (MOV DPTR,#data16) or 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 during the fetching operation code or when operating on data from program
memory. Note: The program counter is not mapped to the SFR area.
Port Registers:
The I/O ports are controlled by Special Function Registers
. The
contents of the SFR can be observed on corresponding pins on the chip. Writing a 1 to any of the ports
(see
) causes the corresponding pin to be at high level (3.3V), and writing a 0 causes the
corresponding pin to be held at low level (GND). The data direction registers
and
individual pins as input or output pins (see the
section for details).
22
Rev.
1.2
