code in the PIC16F877A using MPLAB in assembly languge which is:

Data reception 2 - the operands 4 bits and the operation 4 OP CODE bits are obtained Through a matrix of buttons (in binary.) You can use buttons 0,1 and C, B, A only. When buttons A and B indicate that you enter the operand A / B and button C indicates That put in an order. The values themselves will be typed using the 0 and 1 buttons. For example C 011, B 1 11, A 001: The LSB in operands A and B will be the sign of the number) + / - ( The first number will be written at the address, the second 0x30 at 0x40 and the type of operation at 0x50. In case of incorrect operation code "ERROR" will be displayed on the display The received numbers must be displayed on the LCD in the top row According to the OP CODE, the ALU unit detects the operation and executes the command.

Sample command list: A. A-B - 001 result in 0x60 (value and mark) B. A * B - 010) multiplication (result in 0x60 c. A / B - 011)only a whole part (result in 0x60 d. A - 100 to the power of B result in 0x60 e. F. 110 The number "0" in B Result at 0x60 The result of the operation must be displayed on the LCD in the second row