These are EPROMs. Unprogrammed, all the bits are high. If some cells are bad, they will remain high when programmed. Or, some cells could fail through age, wear, etc. On Thu, 9 Jul 2015, Rob Eaglestone wrote: > Defective via seven off-by-one errors, but otherwise identical? > > On Wed, Jul 8, 2015 at 10:36 PM, William Levak <wlevak@sdf.org> wrote: > >> >> There are two sets of DOS ROMs for the 8280 on zimmers.net, 30054x-001 >> and 30054x-revA. Comparing these two sets, there are a total of seven >> differences between them. Where they are different, the -001 ROMs are one >> higher than the -revA ROMs. This includes two locations where there are >> $AA fill bytes and the -001 ROMs have two $AB amongst all the $AA. >> It appears that the -001 ROMs are defective. >> >> On Tue, 7 Jul 2015, William Levak wrote: >> >> >>> On zimmers.net there are two 8280 300541 files: 300541-001.bin and >>> 300541-revB.bin. If you compare the two files, everywhere they are >>> different, 300541-001.bin is 2 higher than 300541-revB.bin. If you >>> disassemble them, 300541-revB.bin makes sense; 300541-001.bin does not. >>> >>> Therefore: 300541-001.bin is a version of 300541-revB.bin with a bad d1 >>> line. >>> >>> The schematics do not show a GCR ROM. >>> >>> The schematics are available at: >>> >>> www.cbmhardware.de/floppy/cbm8280.php >>> >>> They are very fuzzy and hard to read. I am working on cleaning up a >>> copy. When it is ready, I will send it to zimmers.net. Don't expect >>> much. It was scanned at a very low resolution. >>> >>> wlevak@sdf.lonestar.org >>> SDF Public Access UNIX System - http://sdf.lonestar.org >>> >>> Message was sent through the cbm-hackers mailing list >>> >>> >> wlevak@sdf.lonestar.org >> SDF Public Access UNIX System - http://sdf.lonestar.org >> >> Message was sent through the cbm-hackers mailing list >> > wlevak@sdf.lonestar.org SDF Public Access UNIX System - http://sdf.lonestar.org Message was sent through the cbm-hackers mailing listReceived on 2015-07-10 19:00:06
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