The document discusses Assembly Language Programming of the 8051 microcontroller. It covers the following key points in 3 sentences: Assembly language uses mnemonics to represent machine code instructions and provides a lower level of programming than high-level languages. The 8051 has 8-bit registers including the accumulator register A used for arithmetic, and 4 status flags in the PSW register for carry, overflow, auxiliary carry, and parity. Assembly language programs are assembled into machine code using an assembler and can access different register banks by setting bits in the PSW register.

1. Assembly Language Programming of 8051

2. Assembly Language Provides ‘English like’ words called ‘mnemonics’ for the machine codes. For e.g. 0010 1111 (2FH), is a 8-bit instruction in Machine language of 8051 to add two numbers ADD A, R7 is an Assembly language instruction of 8051 to add two numbers

3. High-level Languages These languages are machine-independent Programmer may not know the internal details of the CPU For e.g. Embedded C , Embedded Java etc. High-level language programs are translated to machine code using a program called ‘ Compiler ’

4. Programming using ‘Assembly’ A program called ‘ Assembler ’ is needed to translate an Assembly Language program to machine language Assembly language is ‘ machine dependent ’, i.e. a low-level programming language A programmer must know the Internal details of CPU Instruction set

5. 8-bit Registers of 8051 These CPU Registers are used to store data temporarily The Accumulator, register A , is used for all Arithmetic & Logic operations. Registers R0 – R7 are for general use Programming Model of 8051 R7 R6 R5 R4 R3 R2 R1 R0 B A

6. Assembly Language program Consists of a series of Assembly language instructions Structure of Assembly Language Has four fields [label:] mnemonic [operands] [;comments] start: MOV R5, #25H ;load 25H in R5 MOV A, #5 ;load 5 in A ADD A, R5 ;add A & R5

7. 8051 Flags and PSW Register The flag register in 8051 is called Program Status Word (PSW)register PSW is a 8-bit register 8051 has 4 conditional flags – CY(Carry), AC(Auxiliary Carry), OV(Overflow), P(Parity) P -- OV RS0 RS1 F0 AC CY D0 D1 D2 D3 D4 D5 D6 D7

8. 8051 Flags CY(Carry Flag) is SET if a carry is generated after addition if a borrow is generated after subtraction Can be SET/CLEARED by using instructions such as SETB C, CLR C AC(Auxiliary Carry Flag) is SET If there is a carry from bit D3 to D4 Used for BCD arithmetic

9. 8051 Flags P(Parity Flag) reflects no. of 1’s in register A SET if ODD no. of 1’s RESET if EVEN no. of 1’s OV(Overflow Flag) Used with signed numbers Detects the overflow of the higher-order bit to the sign bit

10. 8051 Register Banks 8051 has 4 register banks Each bank has 8 registers named R0 to R7 Only one register bank can be accessed by 8051 at a time Bits RS0 & RS1 of PSW register are used to select any one of the four register banks

11. Register Bank Selection bits P -- OV RS0 RS1 F0 AC CY D0 D1 D2 D3 D4 D5 D6 D7 3 2 1 0 Register Bank 18H – 1FH 10H – 17H 08 – 0FH 00 – 07H Address 1 1 0 1 1 0 0 0 RS1 RS0

12. RAM space allocation in 8051 8051 has 128 bytes of RAM RAM address space is 00H to 7FH 8051 RAM is divided into 3 groups Register banks and Stack Bit-addressable memory Scratch Pad memory

13. 00 07 08 0F 10 17 18 1F 20 2F 30 7F Register Bank 0 Register Bank 1 (Stack) Register Bank 2 Register Bank 3 Bit Addressable RAM Scratch Pad RAM RAM Space allocation in 8051

14. Default Register Bank Bank 0 Bank 1 Bank 2 Bank 3 0 1 2 3 4 5 6 7 R0 R1 R2 R3 R4 R5 R6 R7 R0 R1 R2 R3 R4 R5 R6 R7 R0 R1 R2 R3 R4 R5 R6 R7 18 19 1A 1B 1C 1D 1E 1F 10 11 12 13 14 15 16 17 8 9 A B C D E F R0 R1 R2 R3 R4 R5 R6 R7

15. Using RAM addresses MOV R2, #3FH MOV 02, #3FH MOV R1, #85H MOV 01, #85H MOV R0, #99H MOV 00, #99H Bank 0 Q. Which register bank is used by default, when 8051 is powered up? Ans. Register Bank 0 0 1 2 3 4 5 6 7 R0 R1 R2 R3 R4 R5 R6 R7

16. How to switch Register banks? P rogram S tatus W ord Register P -- OV RS0 RS1 F0 AC CY D0 D1 D2 D3 D4 D5 D6 D7 3 2 1 0 Register Bank 18H – 1FH 10H – 17H 08 – 0FH 00 – 07H Address 1 1 0 1 1 0 0 0 RS1 RS0

17. SETB PSW.4 ; select bank 2 MOV R0, #99H MOV R1, #85H MOV R2, #3FH MOV 10, #99H MOV 11, #85H MOV 12, #3FH Bank 2 R0 R1 R2 R3 R4 R5 R6 R7 10 11 12 13 14 15 16 17

18. Assembler Directives are instructions to the Assembler program For e.g. ORG 0H ;start at location 0 begin: MOV R2, #5 ;load 5 in R2 MOV R3, #6 ;load 6 in R3 MOV A, R2 ;copy R2 in A ADD A, R3 ;add A & R3 MOV R4, A ;store result in R4 END ;end of asm source file

19. Assembler Directives Cont. ORG tells Assembler to place the following opcodes starting at memory location 0 END indicates to the Assembler the end of the source code Assembler directives are also called pseudo-instructions No opcodes are generated by assembler for assembler directives

20. Assembling & Running a 8051 program Editor Program Assembler Program Linker Program OH Program Hex file