Alas not in the TRS-80 Model 1 (which is what the first poster is talking about). The 1771 can write 4 types of data markers, later chips (179x, etc) can only do 2 of them. And you guessed it, one of the 'odd' ones is used in the Model 1 on the directory track. For that reason, the double density upgrade board for the model one includes both a 1791 and a 1771. -tony

On 4/29/2006 at 5:53 PM Roy J. Tellason wrote: Not really--the 279x and the 1770/1772 had on-chip data separators (well, so did the 1771, but you didn't want to use it if you expected to function in the real world). 179x used either a 1691-type data separator, a 9216. or a user-supplied one and never made any bones about not having an on-chip one (i.e. there's no XTDS/ pin on a 179x). Back to the TRS-80. I do recall that some versions of TRSDOS used data address mark FA as a directory sector marker, but there are patches to TRSDOS that will use only the F8 mark that later systems used. See Tim Mann's page on the subject: http://www.tim-mann.org/trs80faq.html#[13] And, of course, if you only want to run CP/M on your TRS-80, it don't make no nevermind anyhow. Cheers, Chuck

The 1771 as used in the TRS80 was FM only. It CLAIMED to have a builtin data separator, but those familiar with it consider that claim to be false, at least to the extent of making a large aftermarket for add-on data separator adapter boards. The 179x was both FM AND MFM. BUT,... the 179x could not do some of the data address marks of the 1771 that TRS-DOS required. There were enough perceived incompatabilities, that the Percom "Doubler" (and imitations thereof), instead of replacing the 1771 with a 179x plus trivial glue, put the 1771 and 179x side by side on an adapter board. Many of the imitation "Doubler" boards came with a 1771 already installed. How hard could it be to find one?? -- Grumpy Ol' Fred cisin at xenosoft.com