Note that DA A will not convert a binary number to BCD it produces a meaningful result only as the second step in the addition of two BCD bytes.

(25 / 6 = 4 with a reminder of 1.)įor BCD (binary-coded decimal) arithmetic, ADD and ADDC must be followed by a DA A (decimal adjust) operation to ensure the result is in range for BCD. The A accumulator is left with the value 4 and B accumulator is left with the value 1.

For example if A contains 25 (19H) and B contains 6 (06H), the instructionĭivides the content of A by the content of B. DIV AB divides the accumulator by the data in the B register, leaving the 8-bit quotient in the accumulator and the 8-bit remainder in the B register. The MULAB instruction multiplies the accumulator by the data in the B register and puts the 16-bit product into the concatenated B (high-byte) and accumulator (low-byte) registers. The high- and low-bytes of the DPTR must be decremented separately however, the high-byte (DPH) is only decremented if the low-byte (DPL) underflows from 00H to FFH. Unfortunately, a decrement data pointer instruction is not provided and requires a sequence of instructions such as the following:ĬJNE R7, #OFFH, SKIP IF UNDERFLOW TO FF Since the data pointer generates 16-bit addresses for external memory, incrementing it in one operation is a useful feature. One of the INC instructions operates on the 16-bit data pointer. Increments this value, leaving 41H in location 7FH. For example, if internal RAM location 7FH contains 40H, then the instruction

Any location can be incremented or decremented using direct addressing without going through the accumulator. The 8051 provides powerful addressing of its internal memory space. (Note that one machine cycle takes 1 micro sec if the 8051 is operating from a 12 MHz clock.) Since four addressing modes are possible, the ADD A instruction can be written in different ways:Īll arithmetic instructions execute one machine cycle except the INC DPTR instruction (two machine cycles) and the MUL AB and DIV AB instructions (four machine cycles). The arithmetic instructions are grouped together in Appendix A. The 8051 micro-controller instructions are divided among five functional groups:

Mulab 7 serial number