ST72T311 ST Microelectronics, ST72T311 Datasheet - Page 14

• Manufacturer Part Number: ST72T311
• Description: 8-BIT MCU WITH 8 TO 16K OTP/EPROM
• Manufacturer: ST Microelectronics

ST72E311 ST72T311
2 CENTRAL PROCESSING UNIT
2.1 INTRODUCTION
This CPU has a full 8-bit architecture and contains
six internal registers allowing efficient 8-bit data
manipulation.
2.2 MAIN FEATURES
2.3 CPU REGISTERS
The 6 CPU registers shown in Figure 8 are not
present in the memory mapping and are accessed
by specific instructions.
Figure 8. CPU Registers
14/100
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
8 MHz CPU internal frequency
Low power modes
Maskable hardware interrupts
Non-maskable software interrupt
RESET VALUE = RESET VECTOR @ FFFEh-FFFFh
RESET VALUE = STACK HIGHER ADDRESS
15
15
14
RESET VALUE = 1
PCH
8 7
8
RESET VALUE = XXh
RESET VALUE = XXh
RESET VALUE = XXh
7
7
7
7
1
7
1 1 X 1 X X
1 1 H I
PCL
N Z
0
0
0
0
X
0
0
C
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)
In indexed addressing modes, these 8-bit registers
are used to create either effective addresses or
temporary storage areas for data manipulation.
(The Cross-Assembler generates a precede in-
struction (PRE) to indicate that the following in-
struction refers to the Y register.)
The Y register is not affected by the interrupt auto-
matic procedures (not pushed to and popped from
the stack).
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
CONDITIO N CODE REGISTER
STACK POINTER
X = Undefined Value