Alphabetical List of Instructions
| Operation: | ACALL |
| Function: | Absolute Call Within 2K Block |
| Syntax: | ACALL code address |
| Instructions | OpCode | Bytes | Flags |
| ACALL page0 | 0x11 | 2 | None |
| ACALL page1 | 0x31 | 2 | None |
| ACALL page2 | 0x51 | 2 | None |
| ACALL page3 | 0x71 | 2 | None |
| ACALL page4 | 0x91 | 2 | None |
| ACALL page5 | 0xB1 | 2 | None |
| ACALL page6 | 0xD1 | 2 | None |
| ACALL page7 | 0xF1 | 2 | None |
Description: ACALL unconditionally calls a subroutine at the indicated code address. ACALL pushes the address of the instruction that follows ACALL onto the stack, least-significant-byte first, most-significant-byte second. The Program Counter is then updated so that program execution continues at the indicated address.
The new value for the Program Counter is calculated by replacing the least-significant-byte of the Program Counter with the second byte of the ACALL instruction, and replacing bits 0-2 of the most-significant-byte of the Program Counter with 3 bits that indicate the page. Bits 3-7 of the most-significant-byte of the Program Counter remain unchaged.
Since only 11 bits of the Program Counter are affected by ACALL, calls may only be made to routines located within the same 2k block as the first byte that follows ACALL.
| Operation: | ADD, ADDC |
| Function: | Add Accumulator, Add Accumulator With Carry |
| Syntax: | ADD A,operand |
| ADDC A,operand |
|
|
Description: Description: ADD and ADDC both add the value operand to the value of the Accumulator, leaving the resulting value in the Accumulator. The value operand is not affected. ADD and ADDC function identically except that ADDC adds the value of operand as well as the value of the Carry flag whereas ADD does not add the Carry flag to the result.
The Carry bit (C) is set if there is a carry-out of bit 7. In other words, if the unsigned summed value of the Accumulator, operand and (in the case of ADDC) the Carry flag exceeds 255 Carry is set. Otherwise, the Carry bit is cleared.
The Auxillary Carry (AC) bit is set if there is a carry-out of bit 3. In other words, if the unsigned summed value of the low nibble of the Accumulator, operand and (in the case of ADDC) the Carry flag exceeds 15 the Auxillary Carry flag is set. Otherwise, the Auxillary Carry flag is cleared.
The Overflow (OV) bit is set if there is a carry-out of bit 6 or out of bit 7, but not both. In other words, if the addition of the Accumulator, operand and (in the case of ADDC) the Carry flag treated as signed values results in a value that is out of the range of a signed byte (-128 through +127) the Overflow flag is set. Otherwise, the Overflow flag is cleared.
| Operation: | AJMP |
| Function: | Absolute Jump Within 2K Block |
| Syntax: | AJMP code address |
| Instructions | OpCode | Bytes | Flags |
| AJMP page0 | 0x01 | 2 | None |
| AJMP page1 | 0x21 | 2 | None |
| AJMP page2 | 0x41 | 2 | None |
| AJMP page3 | 0x61 | 2 | None |
| AJMP page4 | 0x81 | 2 | None |
| AJMP page5 | 0xA1 | 2 | None |
| AJMP page6 | 0xC1 | 2 | None |
| AJMP page7 | 0xE1 | 2 | None |
Description: AJMP unconditionally jumps to the indicated code address. The new value for the Program Counter is calculated by replacing the least-significant-byte of the Program Counter with the second byte of the AJMP instruction, and replacing bits 0-2 of the most-significant-byte of the Program Counter with 3 bits that indicate the page of the byte following the AJMP instruction. Bits 3-7 of the most-significant-byte of the Program Counter remain unchaged.
Since only 11 bits of the Program Counter are affected by AJMP, jumps may only be made to code located within the same 2k block as the first byte that follows AJMP.
| Operation: | ANL |
| Function: | Bitwise AND |
| Syntax: | ANL operand1, operand2 |
| Instructions | OpCode | Bytes | Flags |
| ANL iram addr,A | 0x52 | 2 | None |
| ANL iram addr,#data | 0x53 | 3 | None |
| ANL A,#data | 0x54 | 2 | None |
| ANL A,iram addr | 0x55 | 2 | None |
| ANL A,@R0 | 0x56 | 1 | None |
| ANL A,@R1 | 0x57 | 1 | None |
| ANL A,R0 | 0x58 | 1 | None |
| ANL A,R1 | 0x59 | 1 | None |
| ANL A,R2 | 0x5A | 1 | None |
| ANL A,R3 | 0x5B | 1 | None |
| ANL A,R4 | 0x5C | 1 | None |
| ANL A,R5 | 0x5D | 1 | None |
| ANL A,R6 | 0x5E | 1 | None |
| ANL A,R7 | 0x5F | 1 | None |
| ANL C,bit addr | 0x82 | 2 | C |
| ANL C,/bit addr | 0xB0 | 2 | C |
Description: ANL does a bitwise "AND" operation between operand1 and operand2, leaving the resulting value in operand1. The value of operand2 is not affected. A logical "AND" compares the bits of each operand and sets the corresponding bit in the resulting byte only if the bit was set in both of the original operands, otherwise the resulting bit is cleared.
| Operation: | CJNE |
| Function: | Compare and Jump If Not Equal |
| Syntax: | CJNE operand1,operand2,reladdr |
| Instructions | OpCode | Bytes | Flags |
| CJNE A,#data,reladdr | 0xB4 | 3 | C |
| CJNE A,iram addr,reladdr | 0xB5 | 3 | C |
| CJNE @R0,#data,reladdr | 0xB6 | 3 | C |
| CJNE @R1,#data,reladdr | 0xB7 | 3 | C |
| CJNE R0,#data,reladdr | 0xB8 | 3 | C |
| CJNE R1,#data,reladdr | 0xB9 | 3 | C |
| CJNE R2,#data,reladdr | 0xBA | 3 | C |
| CJNE R3,#data,reladdr | 0xBB | 3 | C |
| CJNE R4,#data,reladdr | 0xBC | 3 | C |
| CJNE R5,#data,reladdr | 0xBD | 3 | C |
| CJNE R6,#data,reladdr | 0xBE | 3 | C |
| CJNE R7,#data,reladdr | 0xBF | 3 | C |
Description: CJNE compares the value of operand1 and operand2 and branches to the indicated relative address if operand1 and operand2 are not equal. If the two operands are equal program flow continues with the instruction following the CJNE instruction.
The Carry bit (C) is set if operand1 is less than operand2, otherwise it is cleared.
See Also: DJNZ
| Operation: | CLR |
| Function: | Clear Register |
| Syntax: | CLR register |
| Instructions | OpCode | Bytes | Flags |
| CLR bit addr | 0xC2 | 2 | None |
| CLR C | 0xC3 | 1 | C |
| CLR A | 0xE4 | 1 | None |
Description: CLR clears (sets to 0) all the bit(s) of the indicated register. If the register is a bit (including the carry bit), only the specified bit is affected. Clearing the Accumulator sets the Accumulator's value to 0.
See Also: SETB
| Operation: | CPL |
| Function: | Complement Register |
| Syntax: | CPL operand |
| Instructions | OpCode | Bytes | Flags |
| CPL A | 0xF4 | 1 | None |
| CPL C | 0xB3 | 1 | C |
| CPL bit addr | 0xB2 | 2 | None |
Description: CPL complements operand, leaving the result in operand. If operand is a single bit then the state of the bit will be reversed. If operand is the Accumulator then all the bits in the Accumulator will be reversed. This can be thought of as "Accumulator Logical Exclusive OR 255" or as "255-Accumulator." If the operand refers to a bit of an output Port, the value that will be complemented is based on the last value written to that bit, not the last value read from it.
| Operation: | DA |
| Function: | Decimal Adjust Accumulator |
| Syntax: | DA A |
| Instructions | OpCode | Bytes | Flags |
| DA | 0xD4 | 1 | C |
Description: DA adjusts the contents of the Accumulator to correspond to a BCD (Binary Coded Decimal) number after two BCD numbers have been added by the ADD or ADDC instruction. If the carry bit is set or if the value of bits 0-3 exceed 9, 0x06 is added to the accumulator. If the carry bit was set when the instruction began, or if 0x06 was added to the accumulator in the first step, 0x60 is added to the accumulator.
The Carry bit (C) is set if the resulting value is greater than 0x99, otherwise it is cleared.
| Operation: | DEC |
| Function: | Decrement Register |
| Syntax: | DEC register |
| Instructions | OpCode | Bytes | Flags |
| DEC A | 0x14 | 1 | None |
| DEC iram addr | 0x15 | 2 | None |
| DEC @R0 | 0x16 | 1 | None |
| DEC @R1 | 0x17 | 1 | None |
| DEC R0 | 0x18 | 1 | None |
| DEC R1 | 0x19 | 1 | None |
| DEC R2 | 0x1A | 1 | None |
| DEC R3 | 0x1B | 1 | None |
| DEC R4 | 0x1C | 1 | None |
| DEC R5 | 0x1D | 1 | None |
| DEC R6 | 0x1E | 1 | None |
| DEC R7 | 0x1F | 1 | None |
Description: DEC decrements the value of register by 1. If the initial value of register is 0, decrementing the value will cause it to reset to 255 (0xFF Hex). Note: The Carry Flag is NOT set when the value "rolls over" from 0 to 255.
| Operation: | DIV |
| Function: | Divide Accumulator by B |
| Syntax: | DIV AB |
| Instructions | OpCode | Bytes | Flags |
| DIV AB | 0x84 | 1 | C, OV |
Description: Divides the unsigned value of the Accumulator by the unsigned value of the "B" register. The resulting quotient is placed in the Accumulator and the remainder is placed in the "B" register.
The Carry flag (C) is always cleared.
The Overflow flag (OV) is set if division by 0 was attempted, otherwise it is cleared.
See Also: MUL AB
| Operation: | DJNZ |
| Function: | Decrement and Jump if Not Zero |
| Syntax: | DJNZ register,reladdr |
| Instructions | OpCode | Bytes | Flags |
| DJNZ iram addr,reladdr | 0xD5 | 3 | None |
| DJNZ R0,reladdr | 0xD8 | 2 | None |
| DJNZ R1,reladdr | 0xD9 | 2 | None |
| DJNZ R2,reladdr | 0xDA | 2 | None |
| DJNZ R3,reladdr | 0xDB | 2 | None |
| DJNZ R4,reladdr | 0xDC | 2 | None |
| DJNZ R5,reladdr | 0xDD | 2 | None |
| DJNZ R6,reladdr | 0xDE | 2 | None |
| DJNZ R7,reladdr | 0xDF | 2 | None |
Description: DJNZ decrements the value of register by 1. If the initial value of register is 0, decrementing the value will cause it to reset to 255 (0xFF Hex). If the new value of register is not 0 the program will branch to the address indicated by relative addr. If the new value of register is 0 program flow continues with the instruction following the DJNZ instruction.
| Operation: | INC |
| Function: | Increment Register |
| Syntax: | INC register |
| Instructions | OpCode | Bytes | Flags |
| INC A | 0x04 | 1 | None |
| INC iram addr | 0x05 | 2 | None |
| INC @R0 | 0x06 | 1 | None |
| INC @R1 | 0x07 | 1 | None |
| INC R0 | 0x08 | 1 | None |
| INC R1 | 0x09 | 1 | None |
| INC R2 | 0x0A | 1 | None |
| INC R3 | 0x0B | 1 | None |
| INC R4 | 0x0C | 1 | None |
| INC R5 | 0x0D | 1 | None |
| INC R6 | 0x0E | 1 | None |
| INC R7 | 0x0F | 1 | None |
| INC DPTR | 0xA3 | 1 | None |
Description: INC increments the value of register by 1. If the initial value of register is 255 (0xFF Hex), incrementing the value will cause it to reset to 0. Note: The Carry Flag is NOT set when the value "rolls over" from 255 to 0.
In the case of "INC DPTR", the value two-byte unsigned integer value of DPTR is incremented. If the initial value of DPTR is 65535 (0xFFFF Hex), incrementing the value will cause it to reset to 0. Again, the Carry Flag is NOT set when the value of DPTR "rolls over" from 65535 to 0.
| Operation: | JB |
| Function: | Jump if Bit Set |
| Syntax: | JB bit addr, reladdr |
| Instructions | OpCode | Bytes | Flags |
| JB bit addr,reladdr | 0x20 | 3 | None |
Description: JB branches to the address indicated by reladdr if the bit indicated by bit addr is set. If the bit is not set program execution continues with the instruction following the JB instruction.
| Operation: | JBC |
| Function: | Jump if Bit Set and Clear Bit |
| Syntax: | JB bit addr, reladdr |
| Instructions | OpCode | Bytes | Flags |
| JBC bit addr,reladdr | 0x10 | 3 | None |
Description: JBC will branch to the address indicated by reladdr if the bit indicated by bit addr is set. Before branching to reladdr the instruction will clear the indicated bit. If the bit is not set program execution continues with the instruction following the JBC instruction.
| Operation: | JC |
| Function: | Jump if Carry Set |
| Syntax: | JC reladdr |
| Instructions | OpCode | Bytes | Flags |
| JC reladdr | 0x40 | 2 | None |
Description: JC will branch to the address indicated by reladdr if the Carry Bit is set. If the Carry Bit is not set program execution continues with the instruction following the JC instruction.
See Also: JNC
| Operation: | JMP |
| Function: | Jump to Data Pointer + Accumulator |
| Syntax: | JMP @A+DPTR |
| Instructions | OpCode | Bytes | Flags |
| JMP @A+DPTR | 0x73 | 1 | None |
Description: JMP jumps unconditionally to the address represented by the sum of the value of DPTR and the value of the Accumulator.
| Operation: | JNB |
| Function: | Jump if Bit Not Set |
| Syntax: | JNB bit addr,reladdr |
| Instructions | OpCode | Bytes | Flags |
| JNB bit addr,reladdr | 0x30 | 3 | None |
Description: JNB will branch to the address indicated by reladdress if the indicated bit is not set. If the bit is set program execution continues with the instruction following the JNB instruction.
| Operation: | JNC |
| Function: | Jump if Carry Not Set |
| Syntax: | JNC reladdr |
| Instructions | OpCode | Bytes | Flags |
| JNC reladdr | 0x50 | 2 | None |
Description: JNC branches to the address indicated by reladdr if the carry bit is not set. If the carry bit is set program execution continues with the instruction following the JNB instruction.
See Also: JC
| Operation: | JNZ |
| Function: | Jump if Accumulator Not Zero |
| Syntax: | JNZ reladdr |
| Instructions | OpCode | Bytes | Flags |
| JNZ reladdr | 0x70 | 2 | None |
Description: JNZ will branch to the address indicated by reladdr if the Accumulator contains any value except 0. If the value of the Accumulator is zero program execution continues with the instruction following the JNZ instruction.
See Also: JZ
| Operation: | JZ |
| Function: | Jump if Accumulator Zero |
| Syntax: | JNZ reladdr |
| Instructions | OpCode | Bytes | Flags |
| JZ reladdr | 0x60 | 2 | None |
Description: JZ branches to the address indicated by reladdr if the Accumulator contains the value 0. If the value of the Accumulator is non-zero program execution continues with the instruction following the JNZ instruction.
See Also: JNZ
| Operation: | LCALL |
| Function: | Long Call |
| Syntax: | LCALL code addr |
| Instructions | OpCode | Bytes | Flags |
| LCALL code addr | 0x12 | 3 | None |
Description: LCALL calls a program subroutine. LCALL increments the program counter by 3 (to point to the instruction following LCALL) and pushes that value onto the stack (low byte first, high byte second). The Program Counter is then set to the 16-bit value which follows the LCALL opcode, causing program execution to continue at that address.
| Operation: | LJMP |
| Function: | Long Jump |
| Syntax: | LJMP code addr |
| Instructions | OpCode | Bytes | Flags |
| LJMP code addr | 0x02 | 3 | None |
Description: LJMP jumps unconditionally to the specified code addr.
| Operation: | MOV |
| Function: | Move Memory |
| Syntax: | MOV operand1,operand2 |
| Instructions | OpCode | Bytes | Flags |
| MOV @R0,#data | 0x76 | 2 | None |
| MOV @R1,#data | 0x77 | 2 | None |
| MOV @R0,A | 0xF6 | 1 | None |
| MOV @R1,A | 0xF7 | 1 | None |
| MOV @R0,iram addr | 0xA6 | 2 | None |
| MOV @R1,iram addr | 0xA7 | 2 | None |
| MOV A,#data | 0x74 | 2 | None |
| MOV A,@R0 | 0xE6 | 1 | None |
| MOV A,@R1 | 0xE7 | 1 | None |
| MOV A,R0 | 0xE8 | 1 | None |
| MOV A,R1 | 0xE9 | 1 | None |
| MOV A,R2 | 0xEA | 1 | None |
| MOV A,R3 | 0xEB | 1 | None |
| MOV A,R4 | 0xEC | 1 | None |
| MOV A,R5 | 0xED | 1 | None |
| MOV A,R6 | 0xEE | 1 | None |
| MOV A,R7 | 0xEF | 1 | None |
| MOV A,iram addr | 0xE5 | 2 | None |
| MOV C,bit addr | 0xA2 | 2 | C |
| MOV DPTR,#data16 | 0x90 | 3 | None |
| MOV R0,#data | 0x78 | 2 | None |
| MOV R1,#data | 0x79 | 2 | None |
| MOV R2,#data | 0x7A | 2 | None |
| MOV R3,#data | 0x7B | 2 | None |
| MOV R4,#data | 0x7C | 2 | None |
| MOV R5,#data | 0x7D | 2 | None |
| MOV R6,#data | 0x7E | 2 | None |
| MOV R7,#data | 0x7F | 2 | None |
| MOV R0,A | 0xF8 | 1 | None |
| MOV R1,A | 0xF9 | 1 | None |
| MOV R2,A | 0xFA | 1 | None |
| MOV R3,A | 0xFB | 1 | None |
| MOV R4,A | 0xFC | 1 | None |
| MOV R5,A | 0xFD | 1 | None |
| MOV R6,A | 0xFE | 1 | None |
| MOV R7,A | 0xFF | 1 | None |
| MOV R0,iram addr | 0xA8 | 2 | None |
| MOV R1,iram addr | 0xA9 | 2 | None |
| MOV R2,iram addr | 0xAA | 2 | None |
| MOV R3,iram addr | 0xAB | 2 | None |
| MOV R4,iram addr | 0xAC | 2 | None |
| MOV R5,iram addr | 0xAD | 2 | None |
| MOV R6,iram addr | 0xAE | 2 | None |
| MOV R7,iram addr | 0xAF | 2 | None |
| MOV bit addr,C | 0x92 | 2 | None |
| MOV iram addr,#data | 0x75 | 3 | None |
| MOV iram addr,@R0 | 0x86 | 2 | None |
| MOV iram addr,@R1 | 0x87 | 2 | None |
| MOV iram addr,R0 | 0x88 | 2 | None |
| MOV iram addr,R1 | 0x89 | 2 | None |
| MOV iram addr,R2 | 0x8A | 2 | None |
| MOV iram addr,R3 | 0x8B | 2 | None |
| MOV iram addr,R4 | 0x8C | 2 | None |
| MOV iram addr,R5 | 0x8D | 2 | None |
| MOV iram addr,R6 | 0x8E | 2 | None |
| MOV iram addr,R7 | 0x8F | 2 | None |
| MOV iram addr,A | 0xF5 | 2 | None |
| MOV iram addr,iram addr | 0x85 | 3 | None |
Description: MOV copies the value of operand2 into operand1. The value of operand2 is not affected. Both operand1 and operand2 must be in Internal RAM. No flags are affected unless the instruction is moving the value of a bit into the carry bit in which case the carry bit is affected or unless the instruction is moving a value into the PSW register (which contains all the program flags).
** Note: In the case of "MOV iram addr,iram addr", the operand bytes of the instruction are stored in reverse order. That is, the instruction consisting of the bytes 0x85, 0x20, 0x50 means "Move the contents of Internal RAM location 0x20 to Internal RAM location 0x50" whereas the opposite would be generally presumed.
See Also: MOVC, MOVX, XCH, XCHD, PUSH, POP
| Operation: | MOVC |
| Function: | Move Code Byte to Accumulator |
| Syntax: | MOVC A,@A+register |
| Instructions | OpCode | Bytes | Flags |
| MOVC A,@A+DPTR | 0x93 | 1 | None |
| MOVC A,@A+PC | 0x83 | 1 | None |
Description: MOVC moves a byte from Code Memory into the Accumulator. The Code Memory address from which the byte will be moved is calculated by summing the value of the Accumulator with either DPTR or the Program Counter (PC). In the case of the Program Counter, PC is first incremented by 1 before being summed with the Accumulator.
| Operation: | MOVX |
| Function: | Move Data To/From External Memory (XRAM) |
| Syntax: | MOVX operand1,operand2 |
| Instructions | OpCode | Bytes | Flags |
| MOVX @DPTR,A | 0xF0 | 1 | None |
| MOVX @R0,A | 0xF2 | 1 | None |
| MOVX @R1,A | 0xF3 | 1 | None |
| MOVX A,@DPTR | 0xE0 | 1 | None |
| MOVX A,@R0 | 0xE2 | 1 | None |
| MOVX A,@R1 | 0xE3 | 1 | None |
Description: MOVX moves a byte to or from External Memory into or from the Accumulator.
If operand1 is @DPTR, the Accumulator is moved to the 16-bit External Memory address indicated by DPTR. This instruction uses both P0 (port 0) and P2 (port 2) to output the 16-bit address and data. If operand2 is DPTR then the byte is moved from External Memory into the Accumulator.
If operand1 is @R0 or @R1, the Accumulator is moved to the 8-bit External Memory address indicated by the specified Register. This instruction uses only P0 (port 0) to output the 8-bit address and data. P2 (port 2) is not affected. If operand2 is @R0 or @R1 then the byte is moved from External Memory into the Accumulator.
| Operation: | MUL |
| Function: | Multiply Accumulator by B |
| Syntax: | MUL AB |
| Instructions | OpCode | Bytes | Flags |
| MUL AB | 0xA4 | 1 | C, OV |
Description: Multiples the unsigned value of the Accumulator by the unsigned value of the "B" register. The least significant byte of the result is placed in the Accumulator and the most-significant-byte is placed in the "B" register.
The Carry Flag (C) is always cleared.
The Overflow Flag (OV) is set if the result is greater than 255 (if the most-significant byte is not zero), otherwise it is cleared.
See Also: DIV
| Operation: | NOP |
| Function: | None, waste time |
| Syntax: | No Operation |
| Instructions | OpCode | Bytes | Flags |
| NOP | 0x00 | 1 | None |
Description: NOP, as it's name suggests, causes No Operation to take place for one machine cycle. NOP is generally used only for timing purposes. Absolutely no flags or registers are affected.
| Operation: | ORL |
| Function: | Bitwise OR |
| Syntax: | ORL operand1,operand2 |
| Instructions | OpCode | Bytes | Flags |
| ORL iram addr,A | 0x42 | 2 | None |
| ORL iram addr,#data | 0x43 | 3 | None |
| ORL A,#data | 0x44 | 2 | None |
| ORL A,iram addr | 0x45 | 2 | None |
| ORL A,@R0 | 0x46 | 1 | None |
| ORL A,@R1 | 0x47 | 1 | None |
| ORL A,R0 | 0x48 | 1 | None |
| ORL A,R1 | 0x49 | 1 | None |
| ORL A,R2 | 0x4A | 1 | None |
| ORL A,R3 | 0x4B | 1 | None |
| ORL A,R4 | 0x4C | 1 | None |
| ORL A,R5 | 0x4D | 1 | None |
| ORL A,R6 | 0x4E | 1 | None |
| ORL A,R7 | 0x4F | 1 | None |
| ORL C,bit addr | 0x72 | 2 | C |
| ORL C,/bit addr | 0xA0 | 2 | C |
Description: ORL does a bitwise "OR" operation between operand1 and operand2, leaving the resulting value in operand1. The value of operand2 is not affected. A logical "OR" compares the bits of each operand and sets the corresponding bit in the resulting byte if the bit was set in either of the original operands, otherwise the resulting bit is cleared.
| Operation: | POP |
| Function: | Pop Value From Stack |
| Syntax: | POP |
| Instructions | OpCode | Bytes | Flags |
| POP iram addr | 0xD0 | 2 | None |
Description: POP "pops" the last value placed on the stack into the iram addr specified. In other words, POP will load iram addr with the value of the Internal RAM address pointed to by the current Stack Pointer. The stack pointer is then decremented by 1.
See Also: PUSH
| Operation: | PUSH |
| Function: | Push Value Onto Stack |
| Syntax: | PUSH |
| Instructions | OpCode | Bytes | Flags |
| PUSH iram addr | 0xC0 | 2 | None |
Description: PUSH "pushes" the value of the specified iram addr onto the stack. PUSH first increments the value of the Stack Pointer by 1, then takes the value stored in iram addr and stores it in Internal RAM at the location pointed to by the incremented Stack Pointer.
See Also: POP
| Operation: | RET |
| Function: | Return From Subroutine |
| Syntax: | RET |
| Instructions | OpCode | Bytes | Flags |
| RET | 0x22 | 1 | None |
Description: RET is used to return from a subroutine previously called by LCALL or ACALL. Program execution continues at the address that is calculated by popping the topmost 2 bytes off the stack. The most-significant-byte is popped off the stack first, followed by the least-significant-byte.
| Operation: | RETI |
| Function: | Return From Interrupt |
| Syntax: | RETI |
| Instructions | OpCode | Bytes | Flags |
| RETI | 0x32 | 1 | None |
Description: RETI is used to return from an interrupt service routine. RETI first enables interrupts of equal and lower priorities to the interrupt that is terminating. Program execution continues at the address that is calculated by popping the topmost 2 bytes off the stack. The most-significant-byte is popped off the stack first, followed by the least-significant-byte.
RETI functions identically to RET if it is executed outside of an interrupt service routine.
See Also: RET
| Operation: | RL |
| Function: | Rotate Accumulator Left |
| Syntax: | RL A |
| Instructions | OpCode | Bytes | Flags |
| RL A | 0x23 | 1 | C |
Description: Shifts the bits of the Accumulator to the left. The left-most bit (bit 7) of the Accumulator is loaded into bit 0.
| Operation: | RLC |
| Function: | Rotate Accumulator Left Through Carry |
| Syntax: | RLC A |
| Instructions | OpCode | Bytes | Flags |
| RLC A | 0x33 | 1 | C |
Description: Shifts the bits of the Accumulator to the left. The left-most bit (bit 7) of the Accumulator is loaded into the Carry Flag, and the original Carry Flag is loaded into bit 0 of the Accumulator. This function can be used to quickly multiply a byte by 2.
| Operation: | RR |
| Function: | Rotate Accumulator Right |
| Syntax: | RR A |
| Instructions | OpCode | Bytes | Flags |
| RR A | 0x03 | 1 | None |
Description: Shifts the bits of the Accumulator to the right. The right-most bit (bit 0) of the Accumulator is loaded into bit 7.
| Operation: | RRC |
| Function: | Rotate Accumulator Right Through Carry |
| Syntax: | RRC A |
| Instructions | OpCode | Bytes | Flags |
| RRC A | 0x13 | 1 | C |
Description: Shifts the bits of the Accumulator to the right. The right-most bit (bit 0) of the Accumulator is loaded into the Carry Flag, and the original Carry Flag is loaded into bit 7. This function can be used to quickly divide a byte by 2.
| Operation: | SETB |
| Function: | Set Bit |
| Syntax: | SETB bit addr |
| Instructions | OpCode | Bytes | Flags |
| SETB C | 0xD3 | 1 | C |
| SETB bit addr | 0xD2 | 2 | None |
Description: Sets the specified bit.
See Also: CLR
| Operation: | SJMP |
| Function: | Short Jump |
| Syntax: | SJMP reladdr |
| Instructions | OpCode | Bytes | Flags |
| SJMP reladdr | 0x80 | 2 | None |
Description: SJMP jumps unconditionally to the address specified reladdr. Reladdr must be within -128 or +127 bytes of the instruction that follows the SJMP instruction.
| Operation: | SUBB |
| Function: | Subtract from Accumulator With Borrow |
| Syntax: | SUBB A,operand |
| Instructions | OpCode | Bytes | Flags |
| SUBB A,#data | 0x94 | 2 | C, AC, OV |
| SUBB A,iram addr | 0x95 | 2 | C, AC, OV |
| SUBB A,@R0 | 0x96 | 1 | C, AC, OV |
| SUBB A,@R1 | 0x97 | 1 | C, AC, OV |
| SUBB A,R0 | 0x98 | 1 | C, AC, OV |
| SUBB A,R1 | 0x99 | 1 | C, AC, OV |
| SUBB A,R2 | 0x9A | 1 | C, AC, OV |
| SUBB A,R3 | 0x9B | 1 | C, AC, OV |
| SUBB A,R4 | 0x9C | 1 | C, AC, OV |
| SUBB A,R5 | 0x9D | 1 | C, AC, OV |
| SUBB A,R6 | 0x9E | 1 | C, AC, OV |
| SUBB A,R7 | 0x9F | 1 | C, AC, OV |
Description: SUBB subtract the value of operand and the Carry Flag from the value of the Accumulator, leaving the resulting value in the Accumulator. The value operand is not affected.
The Carry Bit (C) is set if a borrow was required for bit 7, otherwise it is cleared. In other words, if the unsigned value being subtracted is greater than the Accumulator the Carry Flag is set.
The Auxillary Carry (AC) bit is set if a borrow was required for bit 3, otherwise it is cleared. In other words, the bit is set if the low nibble of the value being subtracted was greater than the low nibble of the Accumulator.
The Overflow (OV) bit is set if a borrow was required for bit 6 or for bit 7, but not both. In other words, the subtraction of two signed bytes resulted in a value outside the range of a signed byte (-128 to 127). Otherwise it is cleared.
| Operation: | SWAP |
| Function: | Swap Accumulator Nibbles |
| Syntax: | SWAP A |
| Instructions | OpCode | Bytes | Flags |
| SWAP A | 0xC4 | 1 | None |
Description: SWAP swaps bits 0-3 of the Accumulator with bits 4-7 of the Accumulator. This instruction is identical to executing "RR A" or "RL A" four times.
| Operation: | Undefined Instruction |
| Function: | Undefined |
| Syntax: | ??? |
| Instructions | OpCode | Bytes | Flags |
| ??? | 0xA5 | 1 | C |
Description: The "Undefined" instruction is, as the name suggests, not a documented instruction. The 8051 supports 255 instructions and OpCode 0xA5 is the single OpCode that is not used by any documented function. Since it is not documented nor defined it is not recommended that it be executed. However, based on my research, executing this undefined instruction takes 1 machine cycle and appears to have no effect on the system except that the Carry Bit always seems to be set.
Note: We received input from an 8052.com user that the undefined instruction really has a format of Undefined bit1,bit2 and effectively copies the value of bit2 to bit1. In this case, it would be a three-byte instruction. We haven't had an opportunity to verify or disprove this report, so we present it to the world as "additional information."
Note: It has been reported that Philips 8051 model P89C669 uses instruction prefix 0xA5 to let the user access a different (extended) SFR area.
| Operation: | XCH |
| Function: | Exchange Bytes |
| Syntax: | XCH A,register |
| Instructions | OpCode | Bytes | Flags |
| XCH A,@R0 | 0xC6 | 1 | None |
| XCH A,@R1 | 0xC7 | 1 | None |
| XCH A,R0 | 0xC8 | 1 | None |
| XCH A,R1 | 0xC9 | 1 | None |
| XCH A,R2 | 0xCA | 1 | None |
| XCH A,R3 | 0xCB | 1 | None |
| XCH A,R4 | 0xCC | 1 | None |
| XCH A,R5 | 0xCD | 1 | None |
| XCH A,R6 | 0xCE | 1 | None |
| XCH A,R7 | 0xCF | 1 | None |
| XCH A,iram addr | 0xC5 | 2 | None |
Description: Exchanges the value of the Accumulator with the value contained in register.
See Also: MOV
| Operation: | XCHD |
| Function: | Exchange Digit |
| Syntax: | XCHD A,[@R0/@R1] |
| Instructions | OpCode | Bytes | Flags |
| XCHD A,@R0 | 0xD6 | 1 | None |
| XCHD A,@R1 | 0xD7 | 1 | None |
Description: Exchanges bits 0-3 of the Accumulator with bits 0-3 of the Internal RAM address pointed to indirectly by R0 or R1. Bits 4-7 of each register are unaffected.
See Also: DA
| Operation: | XRL |
| Function: | Bitwise Exclusive OR |
| Syntax: | XRL operand1,operand2 |
| Instructions | OpCode | Bytes | Flags |
| XRL iram addr,A | 0x62 | 2 | None |
| XRL iram addr,#data | 0x63 | 3 | None |
| XRL A,#data | 0x64 | 2 | None |
| XRL A,iram addr | 0x65 | 2 | None |
| XRL A,@R0 | 0x66 | 1 | None |
| XRL A,@R1 | 0x67 | 1 | None |
| XRL A,R0 | 0x68 | 1 | None |
| XRL A,R1 | 0x69 | 1 | None |
| XRL A,R2 | 0x6A | 1 | None |
| XRL A,R3 | 0x6B | 1 | None |
| XRL A,R4 | 0x6C | 1 | None |
| XRL A,R5 | 0x6D | 1 | None |
| XRL A,R6 | 0x6E | 1 | None |
| XRL A,R7 | 0x6F | 1 | None |
Description: XRL does a bitwise "EXCLUSIVE OR" operation between operand1 and operand2, leaving the resulting value in operand1. The value of operand2 is not affected. A logical "EXCLUSIVE OR" compares the bits of each operand and sets the corresponding bit in the resulting byte if the bit was set in either (but not both) of the original operands, otherwise the bit is cleared.