参数资料
型号: ST72121J2T6/XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 16 MHz, MICROCONTROLLER, PQFP44
封装: PLASTIC, TQFP-44
文件页数: 3/87页
文件大小: 1365K
代理商: ST72121J2T6/XXX
11/87
ST72121
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
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
2.3 CPU REGISTERS
The 6 CPU registers shown in Figure 5 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 usedtoholdoperandsand theresults 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
theaddress ofthe next instructiontobeexecuted
by the CPU.Itis madeoftwo 8-bitregisters PCL
(Program Counter Low which is the LSB) and PCH
(Program Counter High which is the MSB).
Figure 5. CPU Registers
ACCUMULATOR
X INDEX REGISTER
Y INDEX REGISTER
STACK POINTER
CONDITION CODE REGISTER
PROGRAM COUNTER
70
1C
11H I
N Z
RESET VALUE = RESET VECTOR @ FFFEh-FFFFh
70
0
7
15
8
PCH
PCL
15
8
70
RESET VALUE = STACK HIGHER ADDRESS
RESET VALUE = 1X
11 X 1 X X
RESET VALUE = XXh
X = Undefined Value
11
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