• I am today’s Featured Engineer at EEWeb.com!

    I’m excited to announced that I am today’s Featured Engineer on the EEWeb.com website.


    The interview was submitted in February so the last paragraph is slightly out of date: You can now in fact buy the Propeddle kit although I don’t have an official web shop at this time. Send an email to jac-at-goudsm-dot-it for more information.


  • Temporary build instructions

    To those who bought a kit at the Parallax Expo:


    I’ve been off the Internet all weekend so I had no way to work on the documentation, and there was just not enough time to get it done today once I got back on the grid.

    I truly appreciate your patience and your trust, it inspires me to keep working on the software, the hardware and the documentation. I assure you, I’m working as hard on it as I can, but unfortunately I have other obligations to my work and my family too. Thank you for understanding.

    What follows is an abbreviated version of the build instructions, without pictures for now. I will post a full version with pictures as soon as I can. Use the rightmost board in my Twitter profile background picture for reference if you wish.

    1. Remove the warning sticker.
    2. Start with the (16) resistors near P0..P15, and then do the (6) resistors around the 65C02. The resistors are small, but there’s not enough space to lay them down so bend one wire and solder them in in “stand-up” fashion. Cut off all the wires EXCEPT the resistor wire that’s near pin 37 of the 65C02. Leave that hanging for now. You will have 3 resistors left over; this is intentional!
    3. Solder the (5) blue decoupling capacitors in the designated places near the IC’s. Cut off the wires but don’t cut the resistor wire yet (if you already cut it before reading this, don’t worry).
    4. Solder the (5) diodes in the designated locations near pin 20 of the 65C02 location. The dark band on the diode (cathode) goes towards the tip of the printed arrows. If you get this wrong, the circuit will not work, so make sure you get this right!
    5. Break the male headers into two pieces of 4 pins and two pieces of 16 pins (if it goes wrong and you end up with more pieces, don’t worry, once they’re soldered they’ll be okay). These headers need to be soldered to the BOTTOM side of the circuit board. The easiest way to do this is to plug the long pins of the unsoldered male headers directly into your Propeller Platform motherboard, and then while the pins are still plugged in, put them through the holes in the Propeddle board and solder them from the top. That way the pins are guaranteed to line up perfectly.
    6. Now, solder the female headers (two 4-pin, two 16-pin) on the top side. If you have another board to plug in on top of Propeddle, you can use the same method as above to align the female headers before you solder them. If you don’t have a board that goes on top (yet), you can also decide not to solder the female headers until you get one.
    7. Solder the IC sockets: do them one at a time and make sure you have the notch on the same side as what’s printed on the circuit board. Solder two corners of each socket first and make sure they’re inserted all the way into the board before you solder all the other pins.
    8. As the sticker said, there is a minor problem with this circuit board: pin 36 is not connected to VCC although it should be. This is why we left the the wire from the resistor near pin 37 uncut: it’s that resistor’s connection to VCC. Bend it over diagonally to pin 36 of the 65C02 and solder it to the 65C02 and cut it off. If you already cut the wire off, simply solder another piece of wire between the resistor and the 65C02 pin and cut it off as needed. Whatever you do, make sure the wire doesn’t touch anything else.
    9. Insert the IC’s into the sockets. You’ll have to bend the pins a little (use your workbench to bend all pins at the same time) to make them fit. I know, the markings on the chips are very hard to read and the smaller IC’s have the same number of pins. To make it easier to recognize the 74HC374, I put it on the foam sideways. The two 74HC244’s are on the foam parallel to the bigger chips. Note, all chips are static sensitive so you probably don’t want to walk around with them on your socks. Just pull them from the foam one by one, bend the pins as needed and insert in sockets.
    10. That’s it! You will notice a couple of unsoldered jumpers and the expansion port connector is not included yet either because there’s nothing that can connect to it yet (I’ll be sure to throw in those connectors with the first expansion boards once they are done). The unused jumpers are to convert the board to 3.3V and to use an original NMOS 6502 (which is not supported at this time but may be interesting for some hobbyists who want an alternative to the 65C02). The extra resistors are to add SYNC and CLK2 connectivity but reduce the video output possibilities; they are also not supported (yet).

    I know some of the soldering points on the circuit board are pretty close together and the solder islands aren’t very big. If soldering is not your thing, or if you aren’t confident that you can solder it together yourself without causing short circuits, contact me I’ll solder it together for you for a small charge plus shipping cost.

    If your Propeddle doesn’t work after you put it together, contact me too (tip: use a flatbed scanner to send me a picture of both sides)! I’ll help you make it run, or I we can arrange for you to send it to me to fix it for you (depending on what’s wrong with it). You will have to pay the shipping cost, though.

    Thanks again.


    PS I will post code here tomorrow. The code is now online on Github.

  • About Propeddle

    Propeddle Rev8 S/N 800
    The Propeddle development circuit board with the Western Design Center 65C02S processor, the Alliance Memory AS6C1008 SRAM module, and glue logic. Not shown are the Parallax Propeller, connectors for video and keyboard, and support electronics. They will all be on one circuit board in the final kit!

    Propeddle is single-board computer, based on the 6502 microprocessor. It’s not an emulator and it’s not a replica of any existing computer — it’s something in between. It uses a real 6502 processor as CPU, and a real SRAM chip as memory. A Parallax Propeller generates the clock and other signals needed by the 6502, and it also controls the memory chip. Furthermore, the Propeller can provide video output (VGA, NTSC or PAL), keyboard input (PS/2 connector) and a serial connection. You could say that the software running on the Propeller determines how the 6502 sees the world; that’s why I use the term “Software Defined Computer”.

    The name “Propeddle” is a contraction of “Propeller” and “Peddle”, in honor of Chuck Peddle, one of the engineers who designed the 6502. Don’t worry, Bill Mensch will also be honored, in a future product!

    Once the design is finished, you’ll be able to purchase Propeddle online as a kit, probably via Tindie. Those who don’t want to buy the kit or want to make some modifications, can build their own: All schematics, PCB designs and software will be open source, distributed under MIT License via GitHub. All components are through-hole so you can even build one on a breadboard. There are no PALs, GALs, CPLD’s, FPGA’s or EPROM’s in the circuit, so you don’t need any special hardware to get started, other than an FTDI cable.

    To develop the Propeddle project, I used a Propeller Platform motherboard and a modified Proto VGA-A/V kit from the Shoppe at Wulfden to connect the video and keyboard. The final Propeddle kit will have everything on one circuit board. All you will need is:

    • The assembled Propeddle hardware
    • A power supply (wall wart)
    • A computer with an FTDI cable or a Parallax Propeller Plug
    • A monitor or TV that can display PAL or NTSC or VGA video
    • A keyboard with a PS/2 connector
    • The Parallax Propeller software, freely available from the Parallax website
    • The Propeddle software available from Github

    Once the final PCB design is done, I’ll probably make all those items available (except the computer 😉 ) or I’ll post links to where you can get them.

    Propeddle was inspired by the Prop6502 project by Dennis Ferron, for which he got an honorable mention in a Parallax contest in 2008. Thanks for sharing, Dennis!

    More information will appear on this website and on the Propeddle Google Plus account. Before the Propeddle website existed, I wrote a lot of information in the SavageCircuits forums; those posts are available on the Zappbots website now.

    Thanks for reading!