ST72321M6 Datasheet, PDF (20/175 Pages) STMicroelectronics – 80-pin 8-bit MCU with 32 to 60 Kbytes Flash, ADC, five timers, SPI, SCI, I2C interface

ST72321M6 ST72321M9
5 CENTRAL PROCESSING UNIT
5.1 INTRODUCTION
This CPU has a full 8-bit architecture and contains
six internal registers allowing efficient 8-bit data
manipulation.
5.2 MAIN FEATURES
■ Enable executing 63 basic instructions
■ Fast 8-bit by 8-bit multiply
■ 17 main addressing modes (with indirect
addressing mode)
■ Two 8-bit index registers
■ 16-bit stack pointer
■ Low power HALT and WAIT modes
■ Priority maskable hardware interrupts
■ Non-maskable software/hardware interrupts
Figure 7. CPU Registers
7
0
RESET VALUE = XXh
7
0
RESET VALUE = XXh
7
0
RESET VALUE = XXh
15
PCH
87
PCL
0
RESET VALUE = RESET VECTOR @ FFFEh-FFFFh
7
0
1 1 I1 H I0 N Z C
RESET VALUE = 1 1 1 X 1 X X X
15
87
0
RESET VALUE = STACK HIGHER ADDRESS
5.3 CPU REGISTERS
The six CPU registers shown in Figure 1 are not
present in the memory mapping and are accessed
by specific instructions.
Accumulator (A)
The Accumulator is an 8-bit general purpose reg-
ister used to hold operands and the results of the
arithmetic and logic calculations and to manipulate
data.
Index Registers (X and Y)
These 8-bit registers are used to create effective
addresses or as temporary storage areas for data
manipulation. (The Cross-Assembler generates a
precede instruction (PRE) to indicate that the fol-
lowing instruction refers to the Y register.)
The Y register is not affected by the interrupt auto-
matic procedures.
Program Counter (PC)
The program counter is a 16-bit register containing
the address of the next instruction to be executed
by the CPU. It is made of two 8-bit registers PCL
(Program Counter Low which is the LSB) and PCH
(Program Counter High which is the MSB).
ACCUMULATOR
X INDEX REGISTER
Y INDEX REGISTER
PROGRAM COUNTER
CONDITION CODE REGISTER
STACK POINTER
X = Undefined Value
20/175