agsb/6502toy

A 6502toy

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Introduction

I seek for learn, not for speed.

I had an Apple II. The Furby was a two 6502 'like' toy. I want make a SBC minimal as my toy.

There are many "clones" Ben Eater, Mike, Maarten, Grant, Álvarez and others.

And a Great support from 6502.org forum and Wilson Mines Co.

This is a board for learn and testing the version for 6502 of Minimal Indirect Thread Code Forth as IMMU

PS.

• Ben Eater made a revival of 6502.
• using ROM, for read-only memory,
• using RAM, for random access memory,
• using REM, for regular eeprom memory,

Road Map

• make all circuit plans
• make a eeprom programmer like Ben Eater, but using arduino mini and change pins used.
• make a nop circuit to test cpus, using a arduino mini and clockvar6502

Hardware

B.O.M

    - 01 x NMOS 6502, or CMOS 65C02
    - 01 x AT28C16, or AT28C64
    - 01 x 62256,
    - 02 x AT24LC512, 
    - 02 x CMOS 6522
    - 01 x CMOS 6551
    - 02 x 74HC00,
    - 01 x 74HC32,
    - 01 x 74HC74
    - 04 x 3k3 Ohm
    - 12 x 0.1 uF
    - 01 x +4.7 uF 
    - 

All devices are CMOS and 5V capable.

Use wire wrap.

Test NMOS-6502, CMOS-65C02,

The actual memory map will be 60k RAM $0000-$EFFF, 2k Devices $F000-$F7FF and $F800-$FFFF 2k ROM.

The board will have one 6551 ACIA and two 6522 VIA inside, with expansion of more 4 devices.

The devices are mapped at $F000, $F010 to $F0F0, reserving 16 bytes for control for each device.

Also using a 3:8 74HC138 decoder, with $0 reserved, $1 ACIA, $2 VIA, $3 VIA, onboard and $4 to $7 at expansion.

A clock board by crystal of 1.8432 for CIA and by 74HC74 of 0.9612 for CPU, with a Real Timer Click as NMI with 10ms delay using a VIA T1 timer.

No video or keyboard, using terminal at USART 19200 8N1, RS-232, vt-100.

Using a LCD 16x2 by I2C, a keyboard with 6 keys, a beeper and a led, for minimal use.

Using I2C and SPI protocols and devices.

The board have 2 8-pins slots for I2C epproms.

Use UEXT interface for USART, I2C, SPI.

Use 65SIB for alternative interface.

Software

At boot, the bios will copy bytes from a I2C 64k eeprom into RAM at $1000 and jump to $1000.

Use a BIOS and Forth,

Use USART for VT100 terminal, Tera-Term or PuTTy at computer.

Bios

generic routines at bios:

- ram2ram,        copy bytes from RAM to RAM
- rem2ram,        copy bytes from REM to RAM
- ram2rem
- getc
- putc
- hitc
- tick_start
- tick_stop

Memory

The first 4k of RAM $0000-$0FFF is reserved for system.

The $03FF 1k reserved for system, and $E0-$FF 32 bytes at page zero.

The Extended Wozniac Monitor uses RAM at $0200-$027F as terminal input buffer and $24-$2B at page zero.

The page $0300-$03FF is a list of references for devices and system (BIOS, MOS) routines.

The pages $0400-$0FFF are reserved for future expansion, programs start at $1000.

The Forth uses RAM from $1000 to $EFFF and $00D0-$00DF 16 bytes at page zero.

Ideas

• The initial memory map was to be like an Apple II, $0000-$BFFF 48k RAM, $C000-$CFFF 4k Devices, $D000-$FFFF 12k ROM.
• Use 64k RAM and take all write as RAM and reads depends of a latch.

Links

https://6502.org

http://wilsonminesco.com/

https://www.ele.uva.es/~jesus/6502copy/proto.html