Assembly Code for PIC16F877 Microprocessor Model

I need a code in assembly for pic16f877 using mplab to build A "model" of a 4-bit microprocessor that includes the following units: ALU, I/O - LCD display, button matrix and memory . Operation description of the units: Data capture - the 2 4-bit operands and the 4-bit CODE OP operation are received through a matrix of buttons (in binary). Only buttons 0,1 and A,B,C can be used. C --- 011, B --- 111, A--- 001: for example The first number will be recorded in the address 30x,0 the second in 40x0 and the type of operation in 50x.0 In case of entering an incorrect operation code, "ERROR" will be shown on the display The received numbers should be displayed on the LCD in the top row According to the CODE OP, the ALU unit recognizes the operation and executes the command 001 - A-B result in 60x0 (value and sign) 010 - B* A (multiplication (result in 60x0 011 - A/B (only a whole part) result in 60x0 100 - A in possession of B result in 60x0 101 – the number "1" in B results in 60x0 110 - the number of "0" in A results in 60x0 The result of the operation must be displayed on the LCD in the second line.