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Browse documentation/Build Guide

rosco_6502 build guide

A 65C02 computer on a single board, built by you from a bare PCB to a monitor prompt. Five soldering stages, lowest parts first, then power-up. The same guide is available as a PDF.

IC1W65C02CPUU1 BANKED RAMU2 LOW RAMU3 ROMIC2 DECODERIC5 DUART GLUEU4 BANKIC3DUART
W65C02CPU at 10 MHz
544 KB + 32 KBRAM + EEPROM
2 × UARTplus SPI / SD
100 × 100 mm379 solder joints
Download PDF

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Read first

Before you solder

Tick the kit off against the packing list, then build in the order of this guide. Low parts go first, so the board always lies flat while you solder.

Which way round

Every map shows the component side with the 2×18 expansion header J5 on the right. Keep your board that way and "left", "right" and "up" in this guide always match what you see.

You need

Temperature-controlled iron with a fine tip, solder 0.6–1 mm, flush cutters, small pliers, multimeter, masking tape. For repairs: flux and solder wick.

Three parts that can go in backwards

NOTCH PIN 1

Chips and sockets

The notch marks the pin 1 end. Match it to the notch printed on the board.

Here: every notch points up.

STRIPE= MINUS LONG LEAD= PLUS

Electrolytic caps

The long lead goes in the hole marked +. The stripe faces away from it.

Here: every stripe faces right.

FLAT EDGE= MINUS SHORT LEAD= MINUS

LEDs

The flat edge of the body sits on the flat of the printed outline.

Here: both flat edges face left.

Every joint

Good

A small cone that wets both the pad and the lead.

Bead on the lead

Solder never reached the pad. Add flux, reheat pad and lead together.

Bridge

Two pads joined. Draw the excess off with wick, then check the gap.

The routine

  1. Heat the pad and the lead together.
  2. Feed solder into the joint, not onto the tip.
  3. Take the solder away, then the iron. Hold still until it sets.
  4. Trim the lead just above the cone.

Static

The chips are static-sensitive. Leave them in their packing until stage 5 and touch something grounded before you handle them.

1
Stage 1 of 5

Resistors

13 parts
26 joints
2K2330R330R
Fit nowAlready fittedLaterNo label on the map = 3K3
ValueQty4 bands5 bandsPositions
3K39orange orange redorange orange black brownR1–R4 R7 R10–R13
2K21red red redred red black brownR8
330R3orange orange brownorange orange black blackR5 R6 R9

How

  1. Resistors have no polarity. Bend both leads at the body, press the part flat on the board, solder, trim.
  2. Finish one value before you open the next bag.

Read the bands from the end where they are grouped. The last band, set apart, is the tolerance.

Look-alikes
3K3 and 330R differ only in the third band: red for 3K3, brown for 330R. Measure one of each before you start.
2
Stage 2 of 5

Small capacitors, crystal

15 parts
32 joints
7pF7pFQ1S1
Fit nowAlready fittedLaterNo label on the map = 100nF
PartQtyMarkedPositions
100nF ceramic11104C1–C4 C8–C12 C15 C19
7pF ceramic27C13 C14, below the crystal
3.6864 MHz crystal13.6864Q1
Button1S1, centre right

How

  1. Nothing in this stage has polarity. Either way round is correct.
  2. Seat each capacitor low on the board. Straighten leads that are wider than the holes with pliers first.
  3. Tape the crystal down and solder it quickly. If a joint will not take, let it cool and try again.
  4. The button only fits one way. Solder all four legs.
Three holes
C13 and C14 have three holes for two leads. One lead always goes in the hole marked ALWAYS below, the other in whichever remaining hole fits the lead spacing.
ALWAYSEITHERALWAYSEITHERQ1
3
Stage 3 of 5

Sockets and oscillator

10 parts
248 joints
X144 402482432282816
Fit nowAlready fittedLaterNumber = pin count
PartQtyPositionsWhich way
40-pin socket1IC1notch up
32-pin socket1U1notch up
28-pin socket2U2 U3notch up
24-pin socket2IC2 IC5notch up
16-pin socket1U4notch up
8-pin socket1IC4notch up
44-pin PLCC socket1IC3cut corner top left
10 MHz oscillator1X1sharp corner bottom left; soldered, no socket

How

  1. Drop the socket in, notch over the printed notch. Solder two opposite corner pins.
  2. Look from the side. Not flat, or notch wrong? Reheat a corner and fix it now.
  3. Solder the remaining pins. It is easy to skip one in a long row.
No chips yet
The sockets stay empty until stage 5.

The oscillator is a metal can with one sharp corner: that is pin 1, usually marked with a dot. It has four legs in an 8-pin outline.

4
Stage 4 of 5

LEDs, headers, power

13 parts
73 joints
GR47010 J5J1J2J3JP1JP2J7
Fit nowAlready fittedLaterG = green, R = red · 470 = 470µF, 10 = 10µF, no label = 100µF
PartQtyPositionsWhich way
LED green1LED1flat edge and short lead left
LED red1LED2flat edge and short lead left
Header 2×181J5short pins into the board
Header 1×63J1–J3short pins into the board
Header 1×22JP1 JP2short pins into the board
100µF electrolytic2C16 C18long lead in + hole (left), stripe right
10µF electrolytic1C20long lead in + hole (left), stripe right
470µF electrolytic1C17long lead in + hole (left), stripe right
DC jack1J7opening to the board edge

How

  1. LEDs first. Solder one lead, check the LED stands straight, then the other.
  2. Headers next. Tack one pin, check the header is upright, then the rest.
  3. Electrolytics, the 470µF last. Push each one flat first.
  4. The DC jack has thick tabs: give each one a few seconds of heat and enough solder to fill the slot.
Polarity
A reversed electrolytic can burst. A reversed LED stays dark. Check each stripe and flat edge against the map before soldering.

J4 and J6 stay empty: no parts are supplied for them.

5
Stage 5 of 5

Chips and jumpers

9 chips
no soldering
IC1 W65C02 CPUU1 AS6C4008 RAMU2 62256 RAMU3 AT28C256 ROMIC2 DECODERIC5 DUART GLUEU4 74HCT174IC4555IC3DUART JP1JP2
Fit nowAlready fittedLaterPosition and chip

First, with the sockets still empty

  1. Check every joint with a magnifier: beads, bridges, skipped pins.
  2. Multimeter on continuity across the two empty holes of J6, bottom right. A brief chirp is the capacitors charging. A steady tone is a short: find it first.

Then the chips

  1. Press each row of legs gently against the bench until both rows are parallel.
  2. Notch to notch, every leg in its hole, then press down evenly.
  3. IC3: cut corner to cut corner (top left), then straight down until it sits level.
Look-alikes
IC2 and IC5 are both ATF22V10C, but each is programmed for its socket: go by the label. U2 and U3 are both 28-pin: U2 is the RAM, U3 the ROM with the firmware label.

Jumpers

Leave JP1 and JP2 open for the first power-up. Park each cap on one pin.

  • JP1 and JP2 power the board from a serial adapter on J1 or J2. Never both, never with a supply on J7.
  • JP3 is a pair of solder pads next to U3. Leave them unbridged.
Last step

Power-up

12 J1 UART AGNDRESET5V IN

J1 pins, left to right:

1GND2RTS3VCC4RXD5TXD6CTS
  1. Power. 5 V DC, regulated, at least 400 mA, centre positive, into J7. Measure the supply before you connect it.
  2. Serial. A USB serial adapter set to 5 V on J1 (UART A). With loose wires: board TXD to adapter RXD, RXD to TXD, GND to GND.
  3. Terminal. 115200 baud, 8 data bits, no parity, 1 stop bit.
  4. Switch on and watch the LEDs.
No protection
Reversed polarity or more than 5 V will destroy chips. There is no fuse and no regulator on the board.

A healthy board

  • LED1, green: blinks about once a second.
  • LED2, red: stays off.

On the terminal

                           ___ ___ ___ ___
___ ___ ___ ___ ___      |  _| __|   |__ |
|  _| . |_ -|  _| . |     | . |__ | | | __|
|_| |___|___|___|___|_____|___|___|___|___|
                  |_____| System
RAM Bankcheck passed
ROM Bank   #0 passed
  Bank   #1 passed
  Bank   #2 passed
  Bank   #3 passed
Memory checks passed
\

The backslash is the WozMon prompt: the board is ready.

Something else happens? Unplug first.

  • Green LED never blinks: measure 5 V across the J6 holes, check the oscillator corner and every notch.
  • A chip gets hot: it is in backwards or in the wrong socket.
  • LED blinks, no text: swap TXD and RXD, check the baud rate, check you are on J1 and not J2.
  • Bankcheck failed: reseat U1 and U4, look for a leg folded under.
  • Garbage on screen: wrong baud rate, or IC2 and IC5 swapped.

Still stuck?

Send clear photos of both sides of the board to Telegram or solderdemon.official@gmail.com and tell us what the two LEDs do.