.. _ue14500:

UE14500
=======

This project is related to the MC14500 one. It is just a 1-bit CPU core that is under consideration as an alternative to the one used in the MC14500 bit-serial processor. It only adds a single register, the carry flag ``CAR``, and replaces the 16 instructions with this alternative set:

.. list-table:: CPU Instructions
    :name: ue14500-instrs
    :header-rows: 1
    
    * - Opcode
      - Instruction
      - Operation
    * - ``0``
      - ``NOPO``
      - No change in RR, C, IEN or OEN
    * - ``1``
      - ``LD``
      - Load RR with Data
    * - ``2``
      - ``ADD``
      - Add Data to RR, CAR
    * - ``3``
      - ``SUB``
      - Subtract by adding complemented Data to RR, CAR
    * - ``4``
      - ``ONE``
      - Force a logic one into the RR and logic zero into CAR
    * - ``5``
      - ``NAND``
      - Logic NOT-AND RR with Data
    * - ``6``
      - ``OR``
      - Logic OR RR with Data
    * - ``7``
      - ``XOR``
      - Logic Exklusive OR RR with Data
    * - ``8``
      - ``STO``
      - Store RR
    * - ``9``
      - ``STOC``
      - Store complemented RR
    * - ``A``
      - ``IEN``
      - Load IEN register with Data
    * - ``B``
      - ``OEN``
      - Load OEN register with Data
    * - ``C``
      - ``JMP``
      - Trigger Jump
    * - ``D``
      - ``RTN``
      - N/A
    * - ``E``
      - ``SKZ``
      - Skip next instruction if RR == 0
    * - ``F``
      - ``NOPF``
      - No change in RR, C, IEN or OEN

------
Pinout
------

.. image:: _static/pinoutue1.png

.. list-table:: Pin description
    :name: pin-description-ue1
    :header-rows: 1
    
    * - Pin #
      - Name
      - Type
      - Summary
    * - ``mprj_io[0]``
      - RSTD
      - I
      - Active low design reset
    * - ``mprj_io[5]``
      - DCLK
      - I
      - Separate design clock input
    * - ``mprj_io[6]``
      - ROM CS
      - IO
      - 1-bit Data Bus
    * - ``mprj_io[10:7]``
      - I[3:0]
      - I
      - Instruction Input
    * - ``mprj_io[11]``
      - WRITE
      - O
      - Output indicating a STO/STOC instruction (Data Write)
    * - ``mprj_io[12]``
      - CAR
      - O
      - Value of CAR register
    * - ``mprj_io[13]``
      - IEN
      - O
      - Value of IEN register
    * - ``mprj_io[14]``
      - JMP
      - O
      - Output indicating a JMP instruction
    * - ``mprj_io[15]``
      - NOPF
      - O
      - Output indicating a NOPF instruction
    * - ``mprj_io[16]``
      - NOPO
      - O
      - Output indicating a NOPO instruction
    * - ``mprj_io[17]``
      - OEN
      - O
      - Value of OEN register
    * - ``mprj_io[18]``
      - RTN
      - O
      - Output indicating a RTN instruction
    * - ``mprj_io[19]``
      - SKIP
      - O
      - Output indicating current instruction is being skipped by a preceding SKP instruction