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Been trying to sort out a few things lately on some of my (ancient) Acorn machines. This Blog entry is tech based, so apologies in advance if it does not make much sense 
In brief, two of these machines have a 8271 disc controller (although this was almost ancient back in the day when these machines were made)
Neither machine will work properly, despite my best efforts. One will not actually initialize at all, I'd guess whatever it is, is holding the CPU in a halt or wait state, I don't have a working oscilloscope* or logic probe to be sure, I just receive a locked cursor at the top of the screen, indicating it has stopped and has not even read the OS rom (as the startup message is not displayed, only a _)
*I have a broken oscilloscope but that's another story
The other one will actually initialize OK now after a lot of cursing swearing and chip swapping, have all the disc logic in place and the filing system rom ( Filing systems came on a rom chip back in those days
) , although they do not have a format command built in.
Some of my later machines do have the format command built in (along with the disc filing system built into the OS) but this is based on the 1770 disc controller. There are a lot of subtle differences, but to avoid a lengthy post about irrelevant things, a 1770 can access both 3.5 and 5.25 floppy drives as well as (with a different FS rom, a sasi (the disc controllers that came before SCSI, way way back) type) , although these (1770 vs 8271) need a different FS rom too blink.gif , whereas a 8271 was designed for 5.25 (more accurately originally for 8") discs. The timing is too slow with an 8271 to reliably access 3.5 discs.
Anyway, it appears that I can format any 5.25 discs with my 1770 based machines, although the 8271 machine cannot read them. I always get an error (error 18) , which indicates a missing track 0 (typically this error would normally arise if you tried to use a new disc without formatting it) , although they are formatted. I think there are some minor differences in the format but not enough to cause this error.
I ended up marking the "non initialising" machine as scrap after wasting many hours with it, so its now for spares only. I'd guess its probably only a chip or two that is faulty, but I don't really feel like de-soldering endless IC logic chips (the only ones remaining are not socketed) on a 25 year old PCB, and then the same again to transplant them into another machine. It had some other faults too, such as a faulty video processor, dodgy keyboard interface circuitry (on the mainboard, not the keyboard) so its best considered "spares only"
So now I have one for spares and one that almost works, its really annoying. I cannot transfer the actual format program across very easily, it "may" be possible via tape ( ) , those of you who have used computers for a long time will remember the days of loading programs from audio tape , but I don't really feel like going back that far (or even dumping it out as hex and manually typing it in either!) , I managed to transfer one section from another machine before via serial (again its RS434 instead of RS232, not too bad) , although this method did format the drive, again it was not readable.
I've not posted about the other horrors I had, such as repairing keyboards (broken tracks and faulty micro switches)
Me thinks I'l turn this into something else and use (another, yes I have another one) and fit the disc logic to that, but I have to make a few other checks first. I think I'll be OK (fingers crossed) but I need to have a major swap around with a lot of internal parts yet again.
In brief, two of these machines have a 8271 disc controller (although this was almost ancient back in the day when these machines were made)
Neither machine will work properly, despite my best efforts. One will not actually initialize at all, I'd guess whatever it is, is holding the CPU in a halt or wait state, I don't have a working oscilloscope* or logic probe to be sure, I just receive a locked cursor at the top of the screen, indicating it has stopped and has not even read the OS rom (as the startup message is not displayed, only a _)
*I have a broken oscilloscope but that's another story
The other one will actually initialize OK now after a lot of cursing swearing and chip swapping, have all the disc logic in place and the filing system rom ( Filing systems came on a rom chip back in those days
) , although they do not have a format command built in.Some of my later machines do have the format command built in (along with the disc filing system built into the OS) but this is based on the 1770 disc controller. There are a lot of subtle differences, but to avoid a lengthy post about irrelevant things, a 1770 can access both 3.5 and 5.25 floppy drives as well as (with a different FS rom, a sasi (the disc controllers that came before SCSI, way way back) type) , although these (1770 vs 8271) need a different FS rom too blink.gif , whereas a 8271 was designed for 5.25 (more accurately originally for 8") discs. The timing is too slow with an 8271 to reliably access 3.5 discs.
Anyway, it appears that I can format any 5.25 discs with my 1770 based machines, although the 8271 machine cannot read them. I always get an error (error 18) , which indicates a missing track 0 (typically this error would normally arise if you tried to use a new disc without formatting it) , although they are formatted. I think there are some minor differences in the format but not enough to cause this error.
I ended up marking the "non initialising" machine as scrap after wasting many hours with it, so its now for spares only. I'd guess its probably only a chip or two that is faulty, but I don't really feel like de-soldering endless IC logic chips (the only ones remaining are not socketed) on a 25 year old PCB, and then the same again to transplant them into another machine. It had some other faults too, such as a faulty video processor, dodgy keyboard interface circuitry (on the mainboard, not the keyboard) so its best considered "spares only"
So now I have one for spares and one that almost works, its really annoying. I cannot transfer the actual format program across very easily, it "may" be possible via tape (
) , those of you who have used computers for a long time will remember the days of loading programs from audio tape , but I don't really feel like going back that far (or even dumping it out as hex and manually typing it in either!) , I managed to transfer one section from another machine before via serial (again its RS434 instead of RS232, not too bad) , although this method did format the drive, again it was not readable.I've not posted about the other horrors I had, such as repairing keyboards (broken tracks and faulty micro switches)
Me thinks I'l turn this into something else and use (another, yes I have another one) and fit the disc logic to that, but I have to make a few other checks first. I think I'll be OK (fingers crossed) but I need to have a major swap around with a lot of internal parts yet again.
