This circuit is designed to solve four arithmetic logic operations between two 8-bit numbers. The numbers are entered from a 4x4 matrix keyboard. The data entered from the keyboard is manipulated with decoders, encoders and registers, to finally reach an ALU. In the ALU one of the operations of addition, multiplication, xor or shift left will be calculated.
The circuit generates a two-bit counter that goes to a decoder, the decoder is responsible for activating the keyboard columns high. Pressing the keyboard columns will cause them to switch from high to low, resulting in the matrix_in input. The data that enter to matrix_in goes to an encoder. The encoder, according to the input, will have as output a hexadecimal value, which will be saved if en_reg is active. When en_reg is active, the data is saved at the address provided by switches 2 to 3. This address is the location where the data will be saved in the register bank.
The operands that enter the ALU are obtained from the register bank, the addresses of these operands are indicated with switches 4 to 5 and 6 to 7. To indicate the ALU operation, switches 0 to 1 are used, depending on the value entered, one of the following operations will be performed:
Finally, the result of the operation is obtained in the 8-bit alu_r output.
After reset, the counter should increase by one every second with a 10MHz input clock.
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | op [1:0] (selects operation) | alu_r [7:0] (operation result) | matrix_in [0:3] (keyboard data) |
| 1 | add_s [3:2] | n/a | en_reg (if active, saves kayboard data in the register bank) |
| 2 | add_op1 [5:4] (defines first operand direction) | n/a | 2bc [1:0] (two bit counter) |
| 3 | add_op2 [7:6] (defines second operand direction) | n/a | z (zero flag) |
| 4 | n/a | n/a | n/a |
| 5 | n/a | n/a | n/a |
| 6 | n/a | n/a | n/a |
| 7 | n/a | n/a | n/a |