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Part II

Part II. The 8051 Assembly Language Stack, Bit Addressing, Arithmetic. A and B Registers. A and B can be accessed by direct mode as special function registers: B – address 0F0h A – address 0E0h - use “ACC” for direct mode. Address Modes.

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Part II

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  1. Part II The 8051 Assembly Language Stack, Bit Addressing, Arithmetic EE/CS-352: Embedded Microcontroller Systems

  2. A and B Registers • A and B can be accessed by direct mode as special function registers: • B – address 0F0h • A – address 0E0h - use “ACC” for direct mode EE/CS-352: Embedded Microcontroller Systems

  3. Address Modes Stack-oriented data transfer – another form of register indirect addressing, but using SP mov sp, #0x40 push 0x55 pop 0x0F0 Note: can only specify RAM or SFRs in direct mode to push or pop. Therefore, to push/pop the accumulator cannot use a: push 0E0h push a EE/CS-352: Embedded Microcontroller Systems

  4. pop Stacks push stack pointer stack EE/CS-352: Embedded Microcontroller Systems

  5. Address Modes Exchange Instructions – two way data transfer XCH a, 0x30 ; a  M[30] XCH a, R0 ; a  R0 XCH a, @R0 ; a  M[R0] XCHD a, @R0 ; exchange “digit” a[7..4] a[3..0] R0[7..4] R0[3..0] Only 4 bits exchanged EE/CS-352: Embedded Microcontroller Systems

  6. Bit-Oriented Data Transfer • SFRs with addresses ending in 0 or 8 are bit-addressable. (80, 88, 90, 98, etc) • Carry flag (C) (bit 7 in the PSW) is used as a single-bit accumulator • RAM bits in addresses 20-2F are bit addressable EE/CS-352: Embedded Microcontroller Systems

  7. Bit Addressable Memory 2F 2E 2D 2C 2B 2A 29 28 20h – 2Fh (16 locations X 8-bits = 128 bits) 27 26 25 24 23 22 21 20 EE/CS-352: Embedded Microcontroller Systems

  8. SFRs that are Bit Addressable SFRs with addresses of multiples of 0 and 8 are bit addressable. EE/CS-352: Embedded Microcontroller Systems

  9. Data Processing Instructions Arithmetic Instructions Logic Instructions EE/CS-352: Embedded Microcontroller Systems

  10. Arithmetic Instructions • Add • Subtract • Increment • Decrement • Multiply • Divide • Decimal adjust EE/CS-352: Embedded Microcontroller Systems

  11. Arithmetic Instructions EE/CS-352: Embedded Microcontroller Systems

  12. ADD Instructions These instructions affect 3 bits in PSW: C = 1 if result of add is greater than FF AC = 1 if there is a carry out of bit 3 OV = 1 if there is a carry out of bit 7, but not from bit 6, or visa versa EE/CS-352: Embedded Microcontroller Systems

  13. Instructions that Affect PSW bits EE/CS-352: Embedded Microcontroller Systems

  14. mov a, #0x3F add a, #0xD3 What is the value of the C, AC, OV flags after the second instruction is executed? ADD Examples EE/CS-352: Embedded Microcontroller Systems

  15. Signed Addition and Overflow 2’s complement: 0000 0000 00 0 … 0111 1111 7F 127 1000 0000 80 -128 … 1111 1111 FF -1 EE/CS-352: Embedded Microcontroller Systems

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