Another versatile floppy disk controller
By a happy coincidence I was able to buy a total of three NEW CompatiCard IV (CC4) on ebay US for very little money in 2019.
The CC4 is a consistent further development of the CC1. The CC2 I leave unmentioned, because it is only a slimmed down version of the CC1 and is actually superfluous.
... Compaticards can be grouped into two broad categories; the I and II; and then the IV. They are very different internally.
The I and II are essentially the same card; they differ in that the I has an external drive connector and supports up to 4 drives. Otherwise, the design is an old-school NEC uPD765A (or Intel 8272A; the same chip) design with external data separator. From a programming viewpoint, the design is of the PC/PC-XT school; the data rate adjustment is not compatible with the PC AT standard and, in fact, uses a completely different I/O port address (e.g. for the first controller, it's 7F2). What this means is that if direct-access utilities use the CC I/II, they must have code to do so, unless the data rate can be set with another utility; i.e., there's nothing at the PC-AT I/O address for adjusting data rate (3F7). So the CC I and II are probably not going to function well with OS/2 or Windows NT (unless someone's done a driver for it).
The IV is very different animal--it uses an "all in one" FDC IC that follows the PC AT conventions. Said FDC is either a NSC PC8477 or an Intel 82077. The two chips are virtually pin-compatible, but the later revisions of the Intel chip (e.g. 82077AA-1) do not really support FM (single-density). The CC IV works well with Windows (all versions) as well as OS/2 and Linux/BSD. It essentially obsoletes the CC I/II cards.
Quote: Chuck Guzis (Chuck(G)), July 21st, 2019: Vintage Computer Federation - VCF
In this quote the most important technical issues are said.
What is new?
Basically the CC4 can do everything that the CC1 can do. New is the support of 2.8 MB drives (3.5") with a data rate of 1 MBit/s. New is also the own BIOS and the switches for easy configuration.
During the DOS boot process, the CC4 immediately detects all connected drives if they have been correctly set with the SW2 switch (own BIOS). This is not the case with CC1. Here the drives are only set up in CONFIG.SYS at the very end.
However, since the 2.8 MB drive has not been accepted in the past, this option is actually superfluous. You also get almost no ED disks today and if only at horrendous prices.
Just because an ebay offer was not sufficiently tagged, I was able to buy a completely shrink-wrapped IBM 10-pack ED 4.0 MB floppy disks (72X6111) for 25 EUR. A „single“ ED disk is normally offered for 10 EUR on ebay!
But watch out! The 2.8 MByte format of the CompatiCard IV is not the official MS-DOS standard format. According to the User's Guide 'is this format unique to CC4DRV and will not be readable with other software packages. These formats were included for people who wish to use the full capacity of the drive'. I can't test this because I don't have another 2.8 MByte drive. The official media descriptor (MD) for the MS-DOS ED format is F0h. The Megamate 2.8 MD is FFh!
In total I use my MegaMate 2.8 (twisted, A2), TAXAN (straight, A3) and Siemens 9775/BASF 6106 (twisted, A2) drives on the external port P4. Important: Power is supplied via lines 1 and 2 of the DB 37 connector! This power connection was already available at the later CC1 cards (1990); not the earlier ones (1987)!
There is nothing more „new“ to say about the CC4. Basically the CC4 has just a very good AT floppy disk controller (SuperFDC) with DD, QD, HD, ED and single density (SD/FM) support.
Besides these three CC4 I have a fourth CC4, which I unfortunately bought months ago for a „lot of money“ on ebay. Who could have guessed that?
With this CC4 the external interface P4 suddenly stopped working after „several“ computer modifications. In other words, my Megamate 2.8 did not make a „sound“ anymore, totally dead. The phrase is coming true again: „Never change a running system."
After some tests I found out that the 5V fuse was broken. So, first I looked for a suitable fuse and ordered it on ebay GB. After two weeks it finally arrived. The old fuse was unsoldered, the new one soldered in and lo and behold, everything works fine again.