555 ALU8 Serial (IEEE)
555 : ALU8 Serial (IEEE)
- Author: Jonathan Cardona Ramírez
- Description: 8-bit serial-in ALU with parallel result and done, zero, negative/sign, carry/borrow, overflow flags (ADD, SUB, AND, OR, XOR, NOT).
- GitHub repository
- Open in 3D viewer
- Clock: 50000000 Hz
How it works
The ALU8 Serial is an 8-bit Arithmetic Logic Unit that processes two operands (A and B) shifted in serially. It supports eight different operations and provides parallel output for the result and status flags.
Operation Sequence:
- Initialization: At the first clock cycle after reset (or when starting a new operation), the ALU latches the operation code (
op[2:0]) and the initialCarry_infrom the input pins. - Operand A: For the first 8 clock cycles, bits are shifted into Operand A (LSB-first) through the
Bit_inpin. - Operand B: For the next 8 clock cycles (cycles 9 to 16), bits are shifted into Operand B (LSB-first) through the
Bit_inpin. - Computation: On the 16th clock cycle, the ALU performs the selected operation on the accumulated operands.
- Completion: The
Donesignal goes high, and the 8-bit result is presented on theuo_outpins. Status flags (Carry, Zero, Negative, Overflow) are updated on the bidirectionaluiopins.
Operations:
000: ADD (A + B + Carry_in)001: SUB (A - B - Carry_in)010: AND (A & B)011: OR (A | B)100: XOR (A ^ B)101: NOT (~A)110: SHL (A << 1, MSB to Carry)111: SHR (A >> 1, LSB to Carry)
How to test
To test the ALU, you can follow these steps:
- Reset: Pulse
rst_nlow to initialize the internal state. - Setup: Set the desired operation on
ui_in[3:1]andCarry_inonui_in[4]. - Shift A: Provide 8 bits of operand A on
ui_in[0], pulsed byclk. - Shift B: Provide 8 bits of operand B on
ui_in[0], pulsed byclk. - Read: After the 16th bit, check
uio_out[4](Done). If high, the result is valid onuo_out[7:0]and flags are onuio_out[3:0].
External hardware
No specific external hardware is required. The design can be interfaced with:
- A microcontroller to automate the serial shifting and result verification.
- Logic analyzers or oscilloscopes to monitor the serial input and parallel output.
- Switches and LEDs for manual testing at low clock frequencies.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | Bit_in (serial data input, LSB-first) | Data_out[0] | Carry_out |
| 1 | op[0] | Data_out[1] | Zero |
| 2 | op[1] | Data_out[2] | Negative |
| 3 | op[2] | Data_out[3] | Overflow |
| 4 | Carry_in | Data_out[4] | Done |
| 5 | Data_out[5] | ||
| 6 | Data_out[6] | ||
| 7 | Data_out[7] |