Testimonials
Last revision of this page: March 5, 2025
TexElec - 34 to 50 Pin 8" Floppy Adapter
When I started with the 8” drives in 2018, there was no plug 'n play adapter for the conversion from 50 pin (from floppy) to 34 pin (to controller). Six years later, the market has sorted this out. Now there are at least five adapters; one of them I designed myself.
The adapter by TexElec is from 2023, is cheap and works fine with my 8" drives. I have just tested it (08/25/2024) with two Mitsubishi M2869-63 connected at the same time (drive A: and B:). I used the CompatiCard IV as the floppy controller.
I have not soft configured the CompatiCard (no cc4drv.sys). I have only set the card and BIOS in my 286 AT to 1.2 MB for drive A: and B:; nothing else. I use a straight 34 pin cable, no twist. The adapters and drives are jumpered to Motor 0 / DS0 for drive A and Motor 1 / DS1 for drive B. That's all.
The CompatiCard IV respectively the PC8477 floppy disk controller is needed for reading and writing in single-density mode (FM).
Particularities
As you can see in the picture on the right, I use the straight cable with a branch and a second cable. This works perfectly. The only peculiarity is that I have equipped both Mitsubishi M286-63 with a terminating resistor of 150 Ω. Normally only the last drive gets a termination resistor. For me, 150 Ω is sufficient. If you still have problems, try 1 kΩ.
This adapter can not handle the so called TG43 (track greater 43) signal. Some 8-inch floppy drives require the TG43 to reduce the write current to the inner tracks of the disk. The CompatiCard IV can not handle/send this signal, too. But, ... the Mitsubishi M286-63 does not need this external signal. The drive has an internal write current switch (SI/SE)
Next the testing with two Tandon TM848-02, same test setup. Here I used two 1 kΩ termination resistors; one on each drive. The only difference is, that the TM848-02 needs an external TG43 signal. For this test, however, it doesn't matter because I don't write more than 43 tracks!
The (or my) Tandon TM848-02 have a little disadvantage in a warm environment. The temperature in my room is 24 °C (75 °F) and U12 (ULM 2074B) is getting very hot; 62 °C (143 °F). Also with two (good) 12V cooling fans the temperature does not go below 42 °C (108 °F).
Testing
I do all my testings with the programm 22DISK by Chuck Guzis. I have the licenced version 1.45 (08/17/2020). Test commands: CFMT, CDIR, DTOC and CTYPE. I test the rotation speed with IMD by Dave Dunflield.
- FM - single density - /A1 - generic CP/M - single sided - 26 x 128 (you need a special FDC)
- MFM - double density - /BIG2 - Big Board 2 - double sided - 15 x 512
- MFM - double density - /BIG6 - Big Board 2 - single sided - 8 x 1024
The picture above shows two 8” drives A: and B: operating simultaneously. This also works very well 90% of the time. However, it has also happened that both drives are suddenly accessed at the same time. This can only be due to the terminating resistor. I have already increased this from 150 Ω to 1 kΩ.
Formatting Under DOS
Under the MS or PC-DOS operating system, 8“ floppy disks cannot be formatted (correctly) because 8” drives only have 76 tracks and not 80. However, this is possible with the help of special programs.
- FDFORMAT by Christoph H. Hochstätter (1991)
- 8FORMAT by Jozef Bogin (2021)
References