What is it?

                            W6502 Dev Board v4.1 © PHB 2021

This BARE board (the last two photos show how it will look once populated) has been designed to allow development of a W65C02, or any other variant of 6502 microprocessor system.

It consists of a Printed Circuit Board with provision for 10 integrated circuits attached. They are: W65C026TPG-14 Western Digital CMOS 6502 14Mhz Microprocessor. MC6850 Motorola 6850 ACIA Asynchronous Communications Interface Adapter. NM27C256Q National Semiconductor 32k x 8 CMOS Eprom. HY62256B Hynix 32k x 8 CMOS Static Ram. SN74LS00 Quad 2 input NAND Gate. SN74LS11 Triple 3 input AND Gate. SN74LS14 Hex Schmitt Inverter. 74LS74AN Dual D-Type Flip Flops. HD74LS138P 1 of 8 Decoder. M74HC163B Synchronous 4 bit counter. Each IC power is decoupled by 0.1uF capacitors.

The system clock is generated by a Crystal Oscillator and is further divided by the flip flops to give /2MHz and /4MHz feeds. The /4Mhz is fed to the CPU and is further divided by the 4 bit counter to give a suitable clock frequency for the ACIA to communicate. a 4Mhz clock at 19200 baud, an 8Mhz clock at 38400 baud. There is also provision for resetting the CPU with a micro button switch and resistor circuit.

The board has a power switch and led to indicate when powered up.

There is a 4 pin connector bottom right of board with crystal closest to you. Connections from left to right are: Gnd-RX-TX-5v.

Along the bottom edge of the board there is provision for a 32 way pin connector. This provides access to the system buses for modification or expansion. From the left to the right the pins are:

D7 D6 D5 D4 D3 D2 D1 D0 A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 CPUCLK PHI2 CPURW CPURESET RAMRW ROMOE ACIACLK /2MHZCLK

The system can be powered from a ‘USB-Serial’ dongle and setting a comms program such as Putty, Hyperterminal or Teraterm to the dongle Com port at 19200-8-N-1 (4Mhz Clock) or 38400-8-N-1 (8Mhz Clock) with no handshaking will work. Pressing the reset button once connected should result in: CEGMON..... A/B/C/E/M/W? on the terminal screen.

The Memory map is as follows:- $0000 - $7FFF 32K x 8 RAM $8000 - $87FF ACIA Control and Status registers $8800 - $8FFF Unused.
$9000 - $FFFF Remainder of Eprom.

I can supply an Eprom for £5 GBP with the following programs pre-loaded:

$A000 - $BFFF Microsoft BASIC 1979 as was supplied with OSI Superboard and Compukit UK101. It has been modified to fix the Garbage Collection routine bug and doesn't prompt for 'Memory Size' as Ram is fixed at 32768 bytes cold start. $C000 - $C7FF UK101 Extended Monitor Program. Modified to be in Eprom. $C800 - $D23F Spare. Set to $FF for future programming. $D240 - $DFFF OSI 6502 Assembler. Modified to be in Eprom. $E000 - $F7FF Spare. Set to $FF for future programming. $F800 - $FFFF Cegmon V2 Monitor. Heavily modified UK101/Superboard monitor to provide Terminal communications through the ACIA and a new menu structure to allow access to (A)ssembler,(B)Assembler Warm Start,(C)old Start Basic,(E)xtended Monitor,(M)onitor and (W)arm Start Basic. NB. Caps Lock must be on!!

Credit must be given to Grant Searle who inspired my quest to build a 6502 based development board and supplied the Cegmon patches to utilise RS232 as opposed to a memory mapped screen. The software supplied is not being sold as I have no legal right to it. It is being included at no extra cost to the hardware in order for the board to be useable as supplied. UK101/Superboard Microsoft Basic, OSI Assembler Extended Monitor, and the Cegmon monitor are available from many sources on the internet either as Hex dumps or source code and there are many other variants of software available for a 6502 running similarly to this board. Experimentation is key.

Why did you make it?

I love 6502 microprocessors and have been programming them for over 40 years. I needed to re-visit those experiences.

What makes it special?

There are very many people who started their interest and/or career using a 6502. This is for them.