MFDC cartridge is a floppy disk drive controller for MSX computers. The controller allows two PC 3.5-inch floppy disk drives to be connected simultaneously, allowing for convenient copying between disks.
The MFDC controller is designed to use standard PC floppy drives, so that you can reuse old floppy drives that you already have, whether in an old computer or one that is lying around in a drawer at home.
The connection is simple, just use the same data cable that was connected to the PC, this is as far as the data cable is concerned. As shown in the photo, the connector has a slot, this slot must match the protrusion of the connector of the data cable itself, thus eliminating the possibility of connecting the cable incorrectly. Additionally, “Pin 1” is also indicated on the label. Pin 1 must match the color marking that all flat ribbon cables have.
On the other hand, we need to get a power supply for our disk drive. The electrical characteristics of the power supply will depend on the parameters of the drive itself (normally indicated on a label on the disk drive itself). As an example, one of my disk drives requires 5V (volts) and a current of 960 mA (milliamps). With this data, we can now look for a power supply that will power the disk drive.
Here you can see the detail of the label on one of my floppy drives:
As a recommendation in the case of amperage (mA), I recommend looking for power supplies that can supply at least double what the label indicates, this way we can make sure that the power supply is powerful enough to absorb the intensity peaks when starting the unit’s motors. If you are going to connect two units you can keep in mind that only one unit will be used at a time, therefore the intensity will never be x2.
The MFDC cartridge is based on a widely known design in the MSX world, the TDC-600, this controller is quite common and you can find different designs on the internet if your intention is to build a controller yourself.
I have chosen to design my own version of the TDC-600, introducing some modifications that I found interesting, which I discuss below:
- Connectivity:
- My design focuses on connectivity with standard PC floppy drives, which are the most common and easy to obtain, and therefore the connectivity scheme is designed to use the same cables as on PCs.
- Reliability:
- The printed circuit board has been completely redesigned by me, the main modifications are focused on the use of more reliable components (such as a packaged oscillator) for example.
- Durability:
- The printed circuit board is made with ENIG finish, for greater durability, as well as electrical characteristics to improve its reliability. For more information about ENIG you can see this article where it is clearly explained what ENIG consists of.
- Features:
- The MFDC includes a selector switch that allows you to choose the operating mode: TDC600 or Custom
- In TDC600 mode the controller works exactly like the original TDC600 design
- In Custom mode a different memory address is used, and the driver is configured to have phantom drive mode disabled by default, thus gaining extra memory for programs
- The MFDC includes a selector switch that allows you to choose the operating mode: TDC600 or Custom
Why a Custom mode?
The main reason is to correct a problem in the original design of the TDC600, which locates its hardware in the first half of page 0 of the memory, which can lead to incorrect operation in some cases. In my experience I have not experienced any notable failures, I have only been able to confirm that when turning on the MSX the floppy drives are activated inappropriately, in some cases they even make a strange noise (and no, I am not talking about the typical noise of the head seek). Investigating further, I have come to determine that in the process of searching for RAM memory, which is carried out by the BIOS, it writes in the registers of the WD37C65/GM82C765 controller chip, which results in the aforementioned behavior.
According to the MSX.org Wiki in Hardware design they comment on these, I quote specifically: »For system extension cartridges, keep any memory-mapped registers above the upper half of the memory frame. IOW, >1FFFh for the frame-0, >5FFFh for the frame-1, >9FFFh for the frame-2 and >DFFFh for the frame-3. Otherwise there’s a risk that software that do dirty RAM search will inadvertently write to the registers of your cartridge and potentially freeze the machine.«
To verify this behavior I have connected a logic analyzer, I have obtained this capture, in which it can be clearly observed that the signals /DS1 and /MO1 behave incorrectly.
Here you can see the detail of the switch that allows you to change the mode. If you want to change the operating mode, you must do so before starting the computer.
Why have a TDC600 mode? Simply to maintain compatibility with programs that access the hardware directly, such as disk copy programs like DSK-PRO Light.
As an extra, an activity LED is included that will light up when data transfers are made. Here you can see the detail, indicated with the word “Data” to refer to the data transfer:
Finally, looking in detail at the part of the printed circuit that connects to the MSX, you can see that the edge has been chamfered, the aim being to improve the insertion of the cartridge into the computer’s expansion slot.
The cartridge is “Homebrew”, this means that I assemble and test it myself, so I can ensure that it works perfectly. If you are interested in purchasing one of these you can do so on the purchase page