Copyright 2024 Laurens Holst
Open and low-cost FlashROM cartridge design for large cartridge games.
- Author: Laurens Holst laurens@grauw.nl
- Site: https://www.grauw.nl/projects/ascii-x/
- Flash tool: https://www.grauw.nl/projects/ascii-x-flash/
- Source: https://github.com/grauw/ascii-x
- Documentation: ASCII16-X specification
- Support: https://www.msx.org/forum/msx-talk/development/ascii-x-flashrom-cartridge
- License: MIT
The ASCII16-X cartridge for MSX is an extension to the common ASCII16 mapper. It provides extended memory capacity, FlashROM memory which allows for persisting save games, mirroring of pages and bank select registers across the entire address space, and is backwards compatible with existing software.
The primary goal of this project is to provide the MSX community with open hardware implementations of ASCII mappers with these extended capabilities, using only commonly available parts, and aimed at optimising manufacturing simplicity and cost. As such, this project also contains actual cartridge hardware implementations built with plain logic ICs.
The following cartridge designs are currently available:
- ASCII16-X Mapper Extra Large (XL) 8 MB
These designs are made with KiCad 9.0.2. Their dimensions target the Overrich cartridge cases. Board width is kept under 10 cm to allow for cheap PCB fabrication. The surface mount components are also all on a single side for cheaper PCB assembly, as well as simplified hand-soldering using a stencil.
- Flash ROM memory with commands for per-sector erasing and programming.
- Extended addressable capacity up to 64 MB (design provided for 8 MB).
- Two 16K mapper pages, mirrored to the full address range.
- Two bank selection registers accessible in all pages.
- Mostly backwards compatible with ASCII16.
See ASCII16-X mapper specification for more information.
This design is suitable for large ROM cartridges of either 4 MB or 8 MB.
Since FlashROMs above 2 MB are only available in 3.3V versions, it requires circuitry for voltage translation between the 5V MSX bus and the 3.3V FlashROM.
The design utilises an Infineon 8 MB FlashROM which is currently the most economical choice, though it also supports smaller capacities. The board has 3 logic ICs for the mapper logic, and 5 additional logic ICs as well as an LDO for the voltage level translation.
The design files can be found in the ASCII16-X Mapper XL folder.
Given enough interest, an ASCII16 design for capacities up to 2 MB could be created. This design can be simplified by omitting the buffers for voltage translation, due to FlashROM chips up to 2 MB being available in 5V versions.
There are no plans for an ASCII16-X design larger than 8 MB. This would need two additional logic ICs or a CPLD or FPGA. At the moment there seems to be no immediate need for it, the current max capacity should be sufficient for now.
Given enough interest, an ASCII8 design for capacities up to 2 MB could also be created. This requires two additional register ICs, but does not need buffers for voltage translation due to FlashROM chips up to 2 MB being available for 5V.
There are no plans for an ASCII8-X design larger than 2 MB. Due to the necessary extra circuitry for mapper registers and 3.3V level translation, it becomes difficult to fit that many chips on the board and keep the costs and complexity low, without resorting to an FPGA. If software makers need access to such large amounts of memory ASCII16-X is the more logical choice.
The designs use SMD chip footprints with relatively fine pin pitches, which requires some skill when hand-soldering. The logic ICs use TSSOP footprints (pin pitch: 0.65 mm), and the FlashROMs use 48-pin TSOP-I (pin pitch: 0.5 mm). For the larger capacities this is pretty much required, however for smaller capacities the designs could be altered to use SOIC and PLCC footprints (pin pitch: 1.27 mm) or even DIP (pin pitch: 2.54 mm).
Bare and assembled boards can be ordered from online services such as PCBWay. It is recommended to use the assembly service offered by the factory, since their assembly fee is very affordable, and they may also be able to source components at better prices.
For convenience the designs are available as PCBWay community projects, batches of (assembled) boards can be ordered directly from them and part of their fee will be donated to yours truly. Feel free to use that service if you wish.
The PCB fabrication and assembly cost depends on many factors, such as batch size, component cost, PCB manufacturer fees, tariffs, and several other factors. However as a rough indication of what to expect; a small batch of around 20 XL units produced in March 2024 cost around US$ 15 apiece (ex. VAT). An estimation of the cost for a batch of 200 units amounts to about US$ 10 apiece (ex. VAT).
Of course for the complete package of a final product there are also additional costs to consider, such as cartridge cases, box, manual, etc.
- Board type: Single pieces
- Different designs: 1
- Size: 99.8 x 65 cm
- Layers: 2 layers
- Material: FR-4
- FR4-TG: TG 150-160
- Thickness: 1.6
- Min track/spacing: 6/6 mil
- Min hole size: 0.3 mm
- Edge connector: Yes
- Beveling: Yes (45°)
- Finish: Immersion gold (ENIG)
- Thickness of immersion gold: 1U"
- Surface finish: Immersion gold (ENIG)
- Thickness of immersion gold: 1U"
- Via process: Tenting vias
- Finished copper: 1 oz Cu
- Remove product no.: Yes
For prototyping in low quantities you can get boards cheaply by selecting the HASL finish, however for distribution you should use ENIG finish even if the PCB cost is higher (roughly 1.5x depending on quantity). Gold plated EDGE fingers are very expensive, so that option is not recommended, ENIG is sufficient.
- Assembly side: Top side
- Contains sensitive components/parts: No
- Accept substitutes made in China: No
When you get a quotation for the assembly, it’s worth cross-checking the parts cost against prices on Digikey or Mouser. You can ask to procure parts from those distributors if there is a significant difference, especially for the expensive parts like the FlashROM.