YACC – Yet Another Custom CPU
Finally time to try building a custom CPU from basic TTL and other “simple” ICs
Bus Connector
Yacc1 will be a multi-board system requiring a motherboard, really more of a basic bus-board, for cards to plug into. For my previous 1802 projects single row breakaway headers with a simple bus-board made of either Veroboard or a simple PCB had all the pins, a grand total of 3X, required. This […]
YACC1 RAM and I/O Control Signals
YACC1 PC Control Signals
YACC1 Addressing modes
Opcode Opcode Rx Opcode Value Opcode [Rx] register points to memory location with data Opcode [M] Memory location points to memory location with data
YACC1 Sequencer Control Signals
A list of control signals the sequencer needs to drive (work in progress). For each general purpose register Load Register Enable Register Output X 4 general purpose registers = 8 signals Program Counter Output Address – Connect PC to address bus Increment PC – Increment the current value of the PC by 1 Load […]
YACC1 General Purpose Register Control Signals
YACC1 Possible parts
All registers should be edge triggered and tri state output (or buffered with a tri-state buffer) 8-bit Registers R0-R3 and Accumulator 74374 Program Counter 74163 Memory 6116 (2k x 8) – Add a page register? Microcode memory? (How wide) Microcode Sequencer?
YACC1 – Instruction Set
This is a total guess Bit 7 = 1 These are the 8 two register instructions where: Bit[6:4] are instruction code Bit[3:2] are destination register, Bit[1:0] are source register MOV Rx Ry 1000 xx yy Cop ADD Rx Ry 1001 xx yy SUB Rx Ry 1010 xx yy 1011 xx […]
YACC1 – Basic Architecture
Here is a first guess at the architecture of the YACC 1 Four general purpose 8-bit registers R0-R3 8-bit Accumulator 8-bit Program Counter 256 bytes x 8 bits memory 256 I/O locations All Instructions are either 8 bits long with immediate and direct addressing modes requiring a 2nd 8-bits