maxtherabbit
Veteran Member
I know right? Makes me feel justified making the thread and not figuring it out myself hithertoWell, that's just...weird. Given that "Verify" is essentially the same as "Read" but without the DMA transfer.
I know right? Makes me feel justified making the thread and not figuring it out myself hithertoWell, that's just...weird. Given that "Verify" is essentially the same as "Read" but without the DMA transfer.
Well I tried it - could scarcely believe my eyes but switching to a modern FDC fixed it. Can format disks with turbo on.I would test with one that is much newer and maybe 16-bit (the floppy port will still work when put into an 8-bit slot). Since the PC/XT only has one clock for both the CPU and the bus, you are running the bus with 7.x MHz as well, but PC/XT cards are made to run at 4.77 MHz. The floppy controller is probably acting up because of that. Note that DOS is VERY picky about track 0, which is most likely why IMD works but DOS format does not. Or maybe IMD is even able to run the floppy disk controller at the correct speed, as it accesses it on a lower hardware level.
NEC D765AC (tried two different samples of this one)Exactly (part number please) is on the FDC that flubs? Intel 8272? NEC 765? No -A?
Inclined to agree but there isn't much else on there except some basic glue logic. How would that break only verify?Those should be fine. So the problem is likely something else on the board.
Is this the original 5150 FDC with the hybrid IBM "cans" on it?Inclined to agree but there isn't much else on there except some basic glue logic. How would that break only verify?
YesThat's an interesting thought, but the 765 has 500 msec idle after index. The usual procedure is to write the track, then use a multi-sector verify on the next rev. Should not be an issue, but it's worth investigating.
Question that I'm not clear on is does the FDC format correctly at 4.77MHz?