Pinky-8

PINKY-8

An affordable, 6502-based SBC for education and retrocomputing that you can build yourself

Note: The image above is of the earlier Revision A board. Revision B has similar dimensions, additional buttons and jumpers, and an improved layout permitting typical corner mounting holes.

When ARM is too much, try PINKY.

Note: The following refers to the Rev B board tag.

Overview

• Uses WDC's updated version of the venerable 6502 8-bit microprocessor for authentic retrocomputing
• 32K of addressable SRAM
• 128K of Flash ROM in 8 jumper-selected, 16K banks
• W65C22S Versatile Interface Adapter supplying 2 x 8-bit bi-directional GPIOs with control lines
• Power-on reset as well as manual reset via push button
• NMI button facilitates debugging and custom functionality
• USB-B receptacle for 5V power, works with any well-regulated phone charger
• Compact 3.5" x 2.8" form-factor
• Uses only through-hole components for easy hand assembly
• Two-sided PCB and minimal componentry make for extremely affordable retrocomputing

Design Approach

Period Appropriate with New Components

PINKY-8 is intended as an affordable educational and/or hobbyist device for those wishing to gain firsthand experience with the historically significant 6502 processor and vintage computer construction. As such, PINKY-8 incorporates chips still in production today that are similar to those found in commercial designs of the late 1970s and early 1980s. Building a PINKY-8 does not require scavenging parts from vintage machines and every bit can easily be soldered by hand.

Minimal but Expandable

PINKY-8 is a barebones SBC with onboard I/O limited to the 2 x 8-bit bi-directional GPIO pins and control lines offered by the 65C22S Versatile Interface Adapter. These are exposed in two 2x7 socket headers into which expansion boards supporting other forms of I/O (e.g. SPI, I2C, video, sound) can be plugged, similar to Arduino shields. There is no elaborate programmable bank switching for RAM or ROM, just jumpers on the board. In lieu of power regulation circuitry, PINKY-8 depends on a well-regulated 5V supply (such as a phone charger) attached via a standard USB A-to-B cable.

Fully Open-Source

PINKY-8 is open-source hardware created with open-source hardware, specifically KiCad 4.0.6. Source for its ROM is located in a separate repository and can be assembled with the open-source CC65 suite.

Specifications

Memory Map

For good performance at minimal cost, address decoding is performed using a single 74AC00 Quad NAND Gate using a scheme advanced by 6502 afficionado, Garth Wilson.

SRAM: $0000-$7FFF (32K)
VIA: $8000-$800F
ROM: $C000-$FFFF (16K)

Clock

Components have been selected to support a maximum clock speed of about 5Mhz. Beyond that faster ROM and RAM are necessary which will considerably increase the cost of a complete board. To approach the W65C02S's 14Mhz maximum rated speed requires very fast RAM into which program data is typically copied from slower ROM at boot by means of still more componentry.

PCB

The board has standard-width traces and drill holes on a two-sided design to facilitate affordable manufacturing by nearly any boardhouse.

Bill of Materials

Required

1 x W65C02S, PDIP-40
1 x W65C22S, PDIP-40
1 x SST39SF010A-70, PDIP-32
1 x AS6C62256-55PCN, PDIP-28
1 x SN74AC00N, PDIP-14
1 x 1-5Mhz 50% Duty Cycle, 10ns Rise Time Oscillator, DIP-8
2 x DS1813-5+ (5% Tolerance), TO-92-3 w/Bent Legs
2 x Tactile Switch 6.0x6.0x4.3mm, Through Hole, 4 Lead
1 x USB B Female Through-Hole Receptacle
6 x 0.1uF 50V MLCC Axial Capacitors
3 x 3.3kOhm 1/4W Axial Metal Film Resistors
1 x 100uF 10V Radial Aluminum Electrolytic Capacitor
3 x 1x3 Pin Header .1" spacing
2 x 2x7 Female Socket Header .1" spacing (can substitute with pin header)
3 x 2-pin Jumper / Shunt, .1" spacing

Optional

2 x DIP-40 Dual wipe or machined sockets
1 x DIP-32 Dual wipe or machined socket
1 x DIP-28 Dual wipe or machined socket
1 x DIP-14 Dual wipe or machined socket
1 x DIP-8 Dual wipe or machined socket
4 x M2.5 standoffs for mounting

Construction

Detailed instructions for board assembly will be added to the wiki in time.