I recently stumbled across the RC2014 retro computer based on the Z80 microprocessor on the Tindie website. Having grown up in the early days of personal computing, this inexpensive computer system looked like a fun project, so I ordered one.
Potential purchasers should know a few things I rapidly learned about this kit. I ordered the “Pro” version of the kit. Documentation exists, but is scattered across the web necessitating some hunting. Print out the pictures for your kit as you find them on the web, as well as the schematics, you will need them. There appears to be at least 3 versions of this kit available, and the boards differ, so your boards may or may not match the web pics you find, or the boards I received.
I would not call this kit suitable for a beginner. The documentation is scattered and presumes a fair knowledge of eight bit retro computer system design. The actually assembly in not overly arduous, though the boards are small. My system went together in three nights, which included correcting my pin installation mistake on my CPU board.
You will need a quality, fine tip soldering iron, preferably with temperature control. I purchased mine from Circuit Specialists on the web. Don’t you dare try to assemble the kit with a soldering gun. You will also need a small pair of edge cutters and a small pair of needle nose pliers. You will also need some very small diameter rosin core solder (try EBAY). If you have a PCB tool to hold the board, it will make assembly easier, but is not required. You might also like to buy a small quantity of single and double row right angle pin headers on EBAY. As I age, my eyesight is declining. There was a time I could read the part number on a tunnel diode, but no longer. I have purchased a small Chinese video microscope on EBAY. No eyepieces to look through, the image is displayed on an LCD screen. This has greatly helped me with the close work, especially looking for un-intended solder bridges. One final helpful tool is an IC pin straightener. This little double-sided plastic tool will drastically reduce the number of bent pins encountered when inserting chips into sockets. It will also relieve you from the “bending IC pins against a table edge” trick.
My kit arrived quite rapidly, considering it shipped from England. It comes in a remarkably small package. The PC boards are all of high quality, as are the components.
I suggest you unpack your kit by board type. My kit contained boards for a backplane, Clock generator, Z80 CPU, ROM, RAM, Serial and Compact flash with CP/M loaded. Also in ROM is Microsoft BASIC, RomWBW, and SCM (Small Computer Monitor). My kit came with a loose collection of parts, and several individually packaged boards with parts. Many of the web pictures show a board with its associated parts arrayed around it. I suggest you try to emulate the pictures with the parts you have.
The female pin connector on the backplane has 40 receptacles for pins. The right angle edge connectors on the board have 40 pins, but only 39 matching mounting holes on the board. So you wind up with one pin hanging off the end of the board. I left this pin on my boards to minimize the possibility of inserting a board one pin off.
Nobody seems to want to tell you what a minimal system consists of. I assume the Compact flash with CP/M is not needed initially. You will need a CPU, Clock generator, Serial board, ROM and RAM.
Nobody seems to want to tell you how to jumper your boards. The pictures will come in very handy. Being able to read a schematic will be an asset as well. I am assuming the shown jumper positions in the board pictures will result in a properly running system, but I don’t know this (yet).
A quick inspection of the boards reveals some have holes for a double row of edge connector pins for the extended RC2014 bus, and some have only a single row of pins. This resulted in my first mistake assembling the kit. Do not mix single row and double row edge connector pins. The proper assembly method for boards with double rows of edge connector pins is to to use the double row pin strips and to remove un-needed pins. A pin is un-needed if there is no corresponding mounting hole in the board. A small pair of needle nose pliers will allow you to grasp pins and, giving a small twist to the pin, pull it free from the black plastic strip. Exercise due care when pulling the pin lest you break the black plastic holder. The pictures do not show this very well. If you do this wrong, you will get to un-solder the mis-installed pins and remove them, possibly damaging your board(s), depending upon your soldering skills.
A hint here, if you assemble the motherboard after installing the edge connector pins on the boards, you can use a female backplane connector to help hold the flexible pin strip straight during board assembly.
Another hint, when installing IC sockets, tack diagonal opposite corners of the socket down with solder. Then, while pressing gently on the socket, reflow the solder on the tacked pins to insure the socket seats directly against the board.
The person that did the PCB layout left little room to bend resistor leads down to fit the PCB holes. You will pretty much have to bend the resistor leads directly down with no radius. So how hard would it have been to leave 1/8 inch on each end of the resistors? Other than this tight spacing, I have nothing to quibble about with the boards. Speaking to quality workmanship, do orient your resistors the same. I prefer to read the color code left to right or top to bottom. It just looks sloppy otherwise.
Some serial board documentation mentions a 68B50 UART. Matching a Motorola serial chip to an Intel/Zilog chip bus seems strange to me. My kit came with a Zilog SIO/2 UART, not the 68B50. While using the RS-232 serial protocol, my board came with no level translator to match the +/- voltage levels of the spec. Something like a MAX232 interface chip is what I expected, but there is no provision for this. Instead an FTDI TTL to USB cable is suggested. Of course, the pictures do not show this cable installed on a serial board. The cable can be installed on the pins with two orientations. Close inspection of the board clearly shows pin 1 labeled ground. My cable has a blue wire in this position on the cable connector, or, flipping the connector over, a red wire. I have no key or marking to ID pin one on the connector, but I have developed a natural aversion to hooking red wires to ground, and have not resolved this yet.
Then too, there is the 5 volt 3 Volt controversy. My serial board will be putting out 5 Volts, retro parts run at 5 Volts. I have no idea what my FTDI cable expects, but if it wants 3 Volts, nothing good will result from connecting the two together. A bit of multimeter sleuthing should shed some light on things.
There is an FTDI cable spec on the web, but the cable seems to be loosely defined to me. My spec has no green wire, but my cable does, so I really don’t know what signal this wire supports. My cable has six positions, and my header on the board has six pins, but some connector diagrams support more connections.
The Pageable ROM card has a set of pads underneath IC U2, a 74HCT138. This chip is a decoder, so it would seem logical that these pads set the I/O address of the card. Of course, nobody tells you what that address should be, or how to jumper the pads to achieve it. I am sure that the software has some definite assumptions about where things are located. So the exploratory path is to consult the schematic and perhaps chase the software assumptions back through the source listings, which are available on the web. Of course, you do have to find the listing that corresponds to the contents of the ROM you have.
I would like to figure out how to duplicate the compact flash module. I would feel much safer if I had a duplicate, lest I damage it. I tried plugging it in to a Compact Flash adapter on my PC, but no dice. Windows 7 does not speak CP/M File structures.
My RC2014 adventure continues. I have serial interface issues, and jumper issues to work through, but problem solving is part of the fun, isn't it.
Addendum: Additional things I have learned that you might like to know:
The FTDI cable sources listed in the SCM manual - the Amazon product listed does not exist, the other source does exist though, with 2-3 days delivery. As I look at the FTDI cables, the pinout seems to be inconsistent, I have cables that do not work, so I suggest not substituting the cable.
There are some steps to getting a cable working: Plug the usb end into your computer, leave the other end unconnected for now. If windows recognizes the cable, allow windows to download and install the driver, which may take some time. If windows does not recognize it and there was no software disc supplied, the cable will not work. On my system, the cable comes up as com24, your system may assign a different Com number. Com1 will also probably be offered as an option, with possibly other Com options. I am running TeraTerm to talk to the system. Run TeraTerm without and with the cable inserted into your computer. The Com option that comes up when you insert the cable is the one you want to select, it is the Com number for the cable. Re-launch TeraTerm between cable connections to let windows discover it. Note that the cable must be plugged in for windows to recognize it and present the option of selecting it in the TeraTerm dialog. If windows can see the cable, select it in the serial dialog. Then select "setup - serial port" and set the baud rate to 115200 baud. Now press reset on the RC2014 and the program selected on the Pageable ROM board should sign on.
TeraTerm is prone to getting confused. Every time you power down the RC2014 Pro system or make changes, you should go through the steps of re-launching TeraTerm, selecting Serial protocol, the correct serial channel, and setting the baud rate. Setting it up once and forgetting about it does not work.
I had originally thought I did not want to mess with FTDI, I knew RS-232, and better the devil you know than the one you don't. So I looked at building a little MAX232 driver board for RS-232. Looking up the specs, the MAX part has maximum throughput limitations, which do not include 115200 baud. Looking further, there are slew rate limitations in the RS-232 spec. At 115200 baud, you are pushing north of 1 Mega bit / second through the link. 1488 / 1489 chips in standard and cmos versions do not meet this limitation. So I gave up, 115200 baud is just too fast for more traditional interfaces. I am not convinced that 115200 baud can be attained within RS-232 specs. FTDI, once figured out, does seem to work quite well.
I had a question about mystery pads under some chips on some boards, their purpose and how to use them. There are signals on some chips that currently are not used. These pads are broken out for possible future use and can be safely ignored. So - Ignore pads under chips.
I have had some difficulty figuring out the bus and connector pinouts, but I think I have finally got a handle on it. I think the problem revolves around standard and enhanced backplanes. The Pro kit, which I assembled, comes with a backplane that supports the enhanced bus. This means there is a second row of female connectors on the backplane to support additional signals (the "enhanced" bus). Not all backplanes support the enhanced bus and not all modules do either. The Pageable ROM and 64K Ram boards need a signal to disable lower Ram when it is desired to have the ROM appear there. This signal appears on pin 4 of the pins above the male bus pins on the module. Unfortunately, the boards supplied with the Pro kit (Pageable ROM and 64k RAM) are not supplied with dual row pins to allow the signal to be passed over the enhanced bus. These boards are supplied with single row male bus pins and a jumper strip of pins. If you assemble them with the parts supplied, you will be assembling the boards for a non-enhanced bus. This requires a jumper wire between the ROM and RAM boards on pin 4 of the jumper pins of each board to pass the RAM disable signal. You can see this jumper wire in some of the pictures available on the internet. This jumper wire is not supplied. The boards with the jumper wire can plug into and work with either standard or enhanced backplanes. You can procure dual row male pins and use them on the modules instead of a jumper wire, passing the signal over the enhanced bus. Then the boards will be properly set up for an enhanced bus (which you have with the Pro kit), but the boards will not be backwards compatible with a non-enhanced bus backplane (which you may not have). Note that if you do install dual row male pins on the modules, you will not have pins to connect a jumper wire to.
You might think that if you assemble the boards with the parts supplied, all will work together as intended. This is not the case for the Pro kit. You will either need to procure a jumper wire or a couple of strips of dual row male pins (try Ebay), it is your choice, but assembling modules as supplied will not work.
The board and software work beautifully. They do need rebooting on start up as the power supplies come to life in the wrong sequence sometimes.
The board requires converters for the HDMI and keyboard (USB) connectors these are rather messy. I converted the board to lay flat and parallel with the backplane board. This gives a tidier arrangement but the board then needs a couple of extra mounting holes to fasten it to the baseboard.
Documentation could address the keyboard interface and the fact that HDMI can be used as well as the composite output to an older TV.
I've been in to "retro home computers" for a long time... Lots of experience soldering, trouble-shooting, designing & making my own boards and custom cases, but next to no experience with CP/M. To my pleasant surprise my daughter has developed an interest in the nuts & bolts of computers, but being 14 has little nostalgia for the 70's and 80's. As as result I thought I'd design a CP/M capable computer for the two of us to build that would be her's to tinker with, based on Grant Searle's design... ...given my total newness to CP/M, and having come across the excellent RC2014 Pro I decided a ready-made kit would be better for the both of us and so bought one. The backplane design isn't just delightfully old school while giving easy expansion potential but allowed my daughter to tackle the project in manageable chunks.
After about a week of on and off effort my daughter has become pretty decent at soldering and has a fully working machine - she's delighted, and I'm pretty darn pleased with her and the results too. She's looking forward to getting to know it and it's operation better, and is already eyeing up further options - I think Colecovision compatibility is on the cards.
So the RC2014 is an excellent little machine with a lot of potential and on that basis I'm very pleased with it. But at this point I would recommend those new to building electronics to avoid it, and even those with a bit of experience to be very careful indeed when putting this kit together. Why? Well I consider myself to be pretty experienced when it comes to such things but even so the documentation really isn't up to the job for construction, and largely absent when it comes to leading the new user through their first steps.
As we came to the end of the build I found myself on a good few occasions having to desolder and move components about when it became apparent my initial guesses were not always right - the kit comes with no documentation, and while there is a good deal of info on the website it's often hard to track down specifics, the schematics and boards aren't all fully labeled, and there is no build guide. I'm also somewhat glad I just spent a very frustrating weekend getting to know the absolute basics of CP/M for the first time as I suspect my daughter would have rapidly lost interest if that frustration had been hers. Some first steps advice, especially with regard to the basics of file transfer, would have saved hours of frustrated googling on my part.
If I may be so bold to make some suggestions. Build: -An included build manual would be wonderful but a proper on-line one would do just fine and is certainly needed -Labeled components would, again, be wonderful but a board-by-board BOM list would be fine if included with the above guide -No urgency, but the next run of boards could do with including component values in all areas to help reduce confusion
Post Build: While I was fortunate enough to spot and rectify all my mistakes and finished up with a working machine... -An initial set up, power on, and basic trouble-shooting guide would be very helpful
First Steps: It would be REALLY helpful if there was also a simple first steps guide... -Want to run BASIC / CP/M? Here's how you set up the computer for that, here's a link to the documentation for this version of BASIC or CP/M, and most important of all here's a quick run-down (with examples) of some commands and software you will need to start using the machine - saving / loading / file transfer basics comes instantly to mind -A list of links to appropriate software would also be very helpful - google is fine but if you've never seen a tree before it's hard to tell one from another and the difference is often important.
To be upfront: it all, finally, went up in smoke and down the trash bin, after wasting me many hours. And while I would consider myself an "advanced amateur", not a professional at all, I cannot, in good faith, recommend this kit to others.
Let us start with the documentation: essentially, that is consists of various scraps of information all over this website and the author's, which in some way correlate, in some way contradict, and mostly require you to squint your eyes and try to figure out from the photos of the various components, HOW, just HOW are you supposed to place said various components. (Want a live example? Look at the parts and try to figure out which of them have double pins and which of them have single pins.) The documentation is, essentially, as bad as possible.
Now the kit: now, you might assume, if the documentation is so bad, perhaps the parts are quite obvious to put together. Well: that is NOT the case. There are pin holes where NO components should be soldered, although this is drawn on the PCB. The pins of the components don't quite fit the holes in the motherboard, and you have to be careful where you place the "starting pin". (That defies the VERY POINT of a motherboard! And of the drawing on PCBs! WHY would you draw double pins if single pins are required?)
Furthermore, it contains apparently no such thing as fail-safe mechanisms, if anything "happens" anywhere — which is super likely due to the one million solder points and the terrible documentation and the unclear kit markings. Anything goes wrong — your kit burns, as did mine (burns = the chips start to smoke and make a glistering sound).
And to be frank: you cannot say "there is no handholding" or "this requires experience", just as you cannot sell a heap of scrap.metal and say, "a little refreshment and this is a car". This is supposed to be a KIT, and it is not cheap!
As to the gentleman himself: a brilliant mind, extremely caring and fast in his replies, an absolute pleasure to deal with. — But you understand, legally, this should be a "point-in-time" contract, such is the nature of buying and selling; one should NOT NEED to contact him. His service to his buyers is GREAT. His product is NOT.
I shall buy another kit some day, I like your IDEA. I am only hoping this will motivate you to a better EXECUTION. Do not take this review unkindly, it is not meant so.
Meanwhile, I got that kit that sounds like a Greek letter (the author surely gets the hint), and — guess what — it works flawlessly.
Some PCBs have silkscreen print not readable, but due to documentation and small cards it is not a real problem. Everything that should be shipped are, and the ROM is in ESD package. (I've recently got other ICs not in ESD packages from other sources..)
Now for my part - ordering the rest of the components and solder everything together...
This has to be probably one of the most complex boards to build, there is a fair bit crammed onto this one.
I did struggle with this one, eventually needing to re flash the avr before it burst into life.
its possible to use it with a rom module installed and in fact it its most stable like this
on a ram only system it can be quite hit and miss, and with the the star trek rom for example I haven't been able to get working, even the ones that have worked it will take multiple goes before it will work - this is a known issue and I'm confident its been worked on but it is something you should bare in mind...
How do enter/output data into/from the system? Dox of this would be very useful. - Do you have a list of methods to perform if/when it is not working? I was working very hard in the early 80s with this Z80 and to make it run under control we had to use an emulator. Do I need one now? I could probably find one on eBay, wright?