glitch
Veteran Member
Remember a number of years ago when Al found that big lot of MXV22 controllers, I bought them to split up, and they turned out to be MXV22Ms? Well, I finally got around to trying to change one over to a MXV22, and it works!
The MXV22M is a QBus controller made by MTI, which talks to 5.25" SA460 drives but presents as a RXV21 compatible interface; that is, RX02 compatible. Bit of a strange choice/format, but I guess it was a way to keep RX02 software compatibility without depending on 8" diskettes.
MTI also made the MXV22, which appears to basically be a 22-bit capable version of their MXV21. Both of these controllers will cable to a Shugart-compatible 8" floppy drive, such as the Shugart SA-800 or Tandon TM-848, and present a RXV21 compatible interface to the QBus. Unlike the MXV22M, the MXV22 and MXV21 are both 100% RX02 compatible: you can read and write diskettes that will interchange with real DEC RX02 subsystems.
The MXV22M purchase was something of an accident, none of us involved realized they were -M suffix variants. Having something that's RX02-alike but doesn't talk to actual 8" diskette drives is far less useful than actual RX01/RX02 media interchange compatibility. Fortunately, NeXT had a MXV22 and was willing to loan it to me (four years ago!) to see about converting the -M suffix modules.
Well, today I had time to set up and test everything. First, I tested NeXT's MXV22 with some RX02 diskettes I'd just prepared yesterday, following my repair of my (at least 12 years dead) RXV21 from my MINC-23. NeXT's controller works fine, it'll even boot from the KDF11-B ROM menu as it supports 22-bit addressing. Now that I knew it worked, I copied all of the jumper changes from the MXV22 to a random MXV22M from the lot I'd purchased. Then I moved the fuse PROMs from NeXT's board to the one I restrapped. There was one jumper I missed at first, and I forgot to close the 22-bit addressing jumper, but after I corrected those, it boots my XXDP 2.5 RX02 test diskette!
Now, the only trouble is, just converting these boards using vintage fuse PROMs is like...$70/ea from Unicorn Electronics, or roll the dice on maybe already programmed fuse PROMs from China. I went ahead and ordered vintage fuse PROMs just to make sure I can really actually copy them (I don't see why I shouldn't be able to, the Data I/O 29B with UniPak 2B supports it), but ultimately I'd like to design a little mezzanine board that uses modern EEPROM or Flash chips to replace the bulk of the fuse PROMs. This may require desoldering the fuse PROM sockets and permanently mounting the mezzanine due to height restrictions, but I don't see that as much of a loss.
As an added bonus, it looks like the MXV22 should be able to format RX02 media directly, without having to use the XXDP or 2.11BSD upconversion utilities!
The MXV22M is a QBus controller made by MTI, which talks to 5.25" SA460 drives but presents as a RXV21 compatible interface; that is, RX02 compatible. Bit of a strange choice/format, but I guess it was a way to keep RX02 software compatibility without depending on 8" diskettes.
MTI also made the MXV22, which appears to basically be a 22-bit capable version of their MXV21. Both of these controllers will cable to a Shugart-compatible 8" floppy drive, such as the Shugart SA-800 or Tandon TM-848, and present a RXV21 compatible interface to the QBus. Unlike the MXV22M, the MXV22 and MXV21 are both 100% RX02 compatible: you can read and write diskettes that will interchange with real DEC RX02 subsystems.
The MXV22M purchase was something of an accident, none of us involved realized they were -M suffix variants. Having something that's RX02-alike but doesn't talk to actual 8" diskette drives is far less useful than actual RX01/RX02 media interchange compatibility. Fortunately, NeXT had a MXV22 and was willing to loan it to me (four years ago!) to see about converting the -M suffix modules.
Well, today I had time to set up and test everything. First, I tested NeXT's MXV22 with some RX02 diskettes I'd just prepared yesterday, following my repair of my (at least 12 years dead) RXV21 from my MINC-23. NeXT's controller works fine, it'll even boot from the KDF11-B ROM menu as it supports 22-bit addressing. Now that I knew it worked, I copied all of the jumper changes from the MXV22 to a random MXV22M from the lot I'd purchased. Then I moved the fuse PROMs from NeXT's board to the one I restrapped. There was one jumper I missed at first, and I forgot to close the 22-bit addressing jumper, but after I corrected those, it boots my XXDP 2.5 RX02 test diskette!
Now, the only trouble is, just converting these boards using vintage fuse PROMs is like...$70/ea from Unicorn Electronics, or roll the dice on maybe already programmed fuse PROMs from China. I went ahead and ordered vintage fuse PROMs just to make sure I can really actually copy them (I don't see why I shouldn't be able to, the Data I/O 29B with UniPak 2B supports it), but ultimately I'd like to design a little mezzanine board that uses modern EEPROM or Flash chips to replace the bulk of the fuse PROMs. This may require desoldering the fuse PROM sockets and permanently mounting the mezzanine due to height restrictions, but I don't see that as much of a loss.
As an added bonus, it looks like the MXV22 should be able to format RX02 media directly, without having to use the XXDP or 2.11BSD upconversion utilities!
