51 special function register of single chip microcomputer

Single chip microcomputer STM32L151CCU6

1206RGB (single)

Photocoupler

Through the study of the previous lessons, we already know that there are ROM, RAM, and parallel I/O ports inside the microcontroller. So, besides these things, what else is there inside the microcontroller? How are these pieces of things connected together?

Let's take a complete analysis of the inside of the microcontroller!

From the figure we can see that there is a CPU inside the 51 MCU for operation and control. There are four parallel I/O ports, which are P0, P1, P2, P3, and ROM, which are used to store programs and have RAM. Used to store intermediate results, in addition to timer/counter, serial I/O port, interrupt system, and an internal clock circuit. There are so many things inside a 51 MCU.

For further analysis of the graph, we know that reading and writing to the parallel I/O port is as long as the data is sent to the latch of the corresponding I/O port, then for the timer/counter, serial I/O How to use the mouth? There are separate memory locations in the microcontroller that are used to control these devices and are referred to as Special Function Registers (SFRs). In fact, we have already touched the special function register of P1. What else? See the table below

symbol

address

Features

B

F0H

B register

ACC

E0H

accumulator

PSW

D0H

Program status word

IP

B8H

Interrupt priority control register

P3

B0H

P3 port latch

IE

A8H

Interrupt enable control register

P2

A0H

P2 port latch

SBUF

99H

Serial port latch

SCON

98H

Serial port control register

P1

90H

P1 port latch

Th1

8DH

Timer/Counter 1 (high 8 bits)

TH0

8CH

Timer/Counter 1 (lower 8 bits)

TL1

8BH

Timer/Counter 0 (high 8 bits)

TL0

8AH

Timer/Counter 0 (lower 8 bits)

TMOD

89H

Timer/counter mode control register

TCON

88H

Timer/counter control register

DPH

83H

Data address pointer (high 8 bits)

DPL

82H

Data address pointer (lower 8 bits)

SP

81H

Stack pointer

P0

80H

P0 port latch

PCON

87H

Power control register

Below, we introduce a few commonly used SFRs.

1, ACC--- is an accumulator, usually denoted by A.

This is something, can't be understood from the name, it is a register, not a thing to do addition, why give it a name? Perhaps it is because one of the numbers must be in the ACC when the operator is doing the operation. Its name is special and its identity is special. We will learn the instructions later in the middle part, and we can find that all the arithmetic instructions are inseparable from it. It has its own zero mark Z, Z = 1 if A = 0, and z = 0 if A ≠ 0. This flag is often used as a condition for the branching of program branches.

2, B - a register.

When you do multiplication or division in multiplication or division, do not do multiplication and division, how to use it.

3, PSW-----program status word. This is a very important thing, which puts a lot of state when the CPU works, so that we can understand the current state of the CPU and handle it accordingly. Please see the table below for its features:

Let's introduce each person's use one by one.

CY: Carry flag. The 8051 operator is an 8-bit arithmetic unit. We know that the 8-bit operator can only represent 0-255. If adding, the two numbers may add more than 255, so the highest bit will be lost. What should I do if I am causing an error in the operation? The highest position will come here. This will be fine. There are advances, borrows, CY=1; no advance, borrow, CY=0

Example: 78H+97H (01111000+10010111)

AC: Auxiliary advance and borrow (bits and borrows between the high nibble and the lower nibble).

Example: 57H+3AH (01010111+00111010)

F0: User flag, determined by the user (programmer) when to use, when not to use.

RS1, RS0: Working register group selection bit. This is what we know.

0V: Overflow flag. The result of the operation is understood by the complement operation. There is overflow, OV=1; no overflow, OV=0. What is overflowing will be covered in the chapters that follow us.

P: Parity: It is used to indicate the parity of the number of binary digits "1" in the ALU operation result. If it is an odd number, P=1, otherwise it is 0. The result of the operation has an odd number of 1, P = 1; the result of the operation has an even number of 1, P = 0.

Example: The result of a certain operation is 78H (01111000). Obviously, the number of 1 is even, so P=0.

4, P0, P1, P2, P3------ This we already know, is the register of four parallel input / output ports. The content inside it corresponds to the output of the pin.

5, IE-----interrupt charge register

Bitwise addressing, address: A8H

EA (IE.7): When EA=0, all interrupts are disabled (ie no interrupt is generated)

When EA=1, the generation of each interrupt is determined by the individual allowable bits.

- (IE.6): Reserved

ET2 (IE.5): Timed 2 overflow interrupt is reserved (for 8052)

ES (IE.4): Serial port interrupt is allowed (ES=1 is allowed, ES=0 is disabled)

ET1 (IE.3): Timed 1 interrupt is allowed

EX1 (IE.2): External interrupt INT1 interrupt is allowed

ET0 (IE.1): Timer 0 interrupt is allowed

EX0 (IE.0): External interrupt INT0 interrupt enable

7, IP-----interrupt priority control register

Bitwise addressing, address bit B8H

6, pointer register

(1) Program Counter PC

Indicates the address of the next instruction to be executed, 16 bits, addressing the 64KB range,

PC = 0000H on reset

(2) Stack pointer SP

Indicates the address of the top element of the stack, 8 bits, which can be set by software. SP = 07H at reset

(3) Data pointer DPtr

@R0, @R1, @DPtr; indicates the unit address of the accessed data memory, 16 bits, and the addressing range is 64 KB. DPtr = DPH + DPL. It can be used to access any unit in the external data memory. If it is not used, it can also be used as a general-purpose register. We decide how to use it. Divided into two registers, DPL (lower 8 bits) and DPH (higher 8 bits). It is used to store 16-bit address values ​​to perform data operations in the 64K byte range for off-chip data RAM or program memory by means of indirect or indexed addressing.

7, timing / counter

(1) Timer mode register: TMOD

(2) Timer Control Register: TCON

(3) Count register: TH0, TL0; Th1, TL1. Can be used to set the initial value of the count.

8052/8032 add special register

(1) Timer 2 control register T2CON; control, set the working mode.

(2) Count register: Th2, TL2

(3) Timer 2 capture/reload registers: RCAP2H, RCAP2L

Store data that is automatically reloaded to Th2 and TL2.