Frequently Asked Questions:
What is ZX-Uno?
Basically it's a FPGA based board focused in the synthesis of ZX Spectrum computer models.
It has the same size of a Raspberry Pi (85.60x56mm) so it would fit into a RasPi case. There are other 8 bit machines in development to be implemented under the same hardware.
What machines would fit into the FPGA?
Firstly it's intended to the whole range of ZX Spectrum machines and extra features like ULAPlus, Turbosound, etc, but also will
accept other machines with the same or less complexity. Only will fit 8 bit machines
with a maximum size of 512Kb between ROM and RAM, with a simple hardware to
shyntetize (nothing about hardware sprites or similar stuff). The core of the
machine is a Xilinx FPGA Spartan XC6SLX9, that it's relatively modest, but big enough to synthetize several 8 bit machines.
Using a bigger FPGA would suposse more machines that can be shyntetized, but also
the price would raise considerably.
Which connectors are included?
The board is designed to use the same enclosures as the Raspberry Pi ones, so the
connectors follow the same layout and are the next:
- Video: Composite video throw RCA connector, RPi case compatible
- Audio: Stereo audio throw a 3.5mm stereo jack, RPi case compatible
- Keyboard: PS/2 connector in the same place of the Ethernet connector in the RPi case
- Power: Regulated 5V throw a micro-USB connector, RPi case compatible
- Joystick: DB9 Atari port, in the same place of USB ports in the RPi case
- Storage: SD card, RPi case compatible
- Tape Load: 3.5mm jack conector, next to the JTAG/RGB connector. Not RPi compatible, you must make the hole
- Expansion: 3x12 female pin header, in the same position of the RPi layout
- RGB and VGA: 9 pin Micro-JST connector in place of HDMI connector of RPi. Custom cable must be made.
- JTAG: 6 pin Micro-JST, internal connector.
Why has no EDGE conector like the original ZX Spectrum?
Well, it just has not it.... yet ;) Basically it exists an electrical incompatibility. The FPGA works at 3.3V and the ZX
Spectrum expansion works at 5V. Also because his compact sized and his “low cost”
price (voltage level shifters would raise the price). Anyway, there is a generic
expansion connector with 36 lines mapped directly in the FPGA, so it's theorically
possible to build an adaptor board with level shifters inside. We are studying it.
Would it be very complex to add USB support (joystick and keyboard)? Nowdays
it's hard to find new PS/2 keyboards and would be nice to have a second joystick.
Yes, it would be complex and also it has incompatible voltage levels. If someone
manages to implement it throw the expansion port, we can add in a future revision
of the board. But now we have to settle with the PS/2 one. Anyway, you can find PS/2 keyboards on shops easily nowadays.
Do I need a special cable?
Only for the prototype, specifically the Xilinx Platform Cable. In the final
version it's not necessary because we'll grant the SD upgrade facility. The rest
of the cables are generic: the power cable is micro-USB, the video one is RCA
and the audio/EAR one are 3.5mm jacks. The only custom cable (like it happens
in all machines) is the RGB/Scart/VGA one, but it isn't very important because the
video quality in the composite signal is excelent thanks to the AD724.
How to use the SD card? Does it allow TZX files or only basic TAP ones?
TZX is a compact audio format that only will work with the EAR port. The systems
that supports TZX (e. g. ResiDOS) really only support a subset of the TZX
specification, essentially the part that is like the TAP files. However TAP
files allways allow loading from mass memory. ZX-UNO use divMMC with ESXDOS ROM, so it supports TAP, SNA and Z80 snapshots, and TRD disk images.
Can I write on tapes or disks (TRD or DSK)?
Since this is not emulation, this possibility depends on the OS that you put on the
ZX Spectrum. ESXDOS can write into TAP files using .TAPEOUT command. In addition, ESXDOS is able to read and write from and to TRD disk images.
About DSK: if any of the OS supports it, then yes; but if not, no. Emulators support
DSK or TRD because they emulate the hardware of the disk drive. Here you could
implement something like that but probably would not fit in the FPGA. To give
you an idea, to support DSK or TRD transparently (without using a special OS that
is who is responsible for it) implies implementing a chip that has the same interface as the uPD765. That is,
records uPD support and physical interface (data bus, CS, etc).
and a system that allow to choose a TRD or DSK image, and this system
must send the information (sector) on demand. That is, we must integrate a
microcontroller that is who is responsible for reading the SD card, present some
kind of OSD menu to choose the image to use, etc.
Does it fit the russian clones or the SAM Coupé?
Very probably yes. Regarding the SAM, in fact it is already implemented partially. It works, apart from some Z80 timing flaws, it loads software via audio IN very well. Furthermore
would fit the ZX80, ZX81, Jupiter ACE (currently implemented too) and some arcades than only have a single Z80
With the upgraded FPGA (Xilinx Spartan-6), bigger than the used in v1 prototypes (Spartan-3), we could port cores of several machines. At this time, they are being developed, some of them work totally or partially: SAM Coupé, Jupiter ACE, Sega Master System, Acorn Atom, Oric Atmos, Vic-20, Apple II, Lady Bug arcade...
How many upgrades are allowed by the chip?
As many upgrades as allow the SPI Flash, I think thousands or houndreds of thousands.
I bought the prototype but I don't know how to solder the SMD components. Any help?
Search it on Google. I found a good tutorial
How much it costs?
I hope that the final board with SMD mounted and connectors unmounted will costs
about 30 euros. The prototype is cheaper because it is not mounted. For my part
I will not increase the cost of the PCB from seeedstudio for prototypes. For the
final version, if the distribution is entrusted to another person, I can not rule
out that there is some benefit, especially since require additional work: welding
connectors, burn firmware, test PCB, packaging, etc...
Upgrade April 2016: Crowdfunding campaign was planned in March 2016.
Final price was 65 euro, shipping costs included. We did our best to maintain the price low.
Who work in the project?
We are 5 guys.
- McLeod. Reviews and proposes, is a de facto partner.
- Superfo. Router, which is responsible for designing the PCB.
- AntonioVillena. Initial idea, scheme design and prototype distribution.
- Quest. Ports of secondary cores. Multiboot system. Firmware and prototypes collaboration
- Hark0. Graphic and web designer.
- What is the license?
Creative Commons Share Alike, that briefly means:
You are free to:
Share — copy and redistribute the material in any medium or format
Under the following terms:
Adapt — remix, transform, and build upon the material
for any purpose, even commercially.
The licensor cannot revoke these freedoms as long as you follow the license terms.
Attribution — You must give appropriate credit, provide a link
to the license, and indicate if changes were made. You may do so in any reasonable
manner, but not in any way that suggests the licensor endorses you or your use.
ShareAlike — If you remix, transform, or build upon the material,
you must distribute your contributions under the same license as the original.
No additional restrictions — You may not apply legal terms or
technological measures that legally restrict others from doing anything the license permits.
You do not have to comply with the license for elements of the material in the
public domain or where your use is permitted by an applicable exception or limitation.
No warranties are given. The license may not give you all of the permissions
necessary for your intended use. For example, other rights such as publicity,
privacy, or moral rights may limit how you use the material.
- Update March 2016:
The crowdfunding campaign was a success thanks to the backers.
Our plan is distribute the 250 ZX-Unos on september, but we'll try to do before
From that moment we trust that has commercial initiatives to sell
it at an affordable price. We only ask them to respect
the license terms: to mention the project is licensed by CC-SA,
name or nickname of the authors and the project website zxuno.com .