PCV v4.1 Doesn't Honor Write Enable Jumper

[chadr]

GW PCB v4.1 will happily write to a disk whether the write enable jumper is on or off. This seems dangerous. Has latest firmware and pulled latest GW software /w pipx.

If I can somehow pull more debug info I will. Just tell me what to do. Thanks.

[GeorgeRudolf]

Not sure what you're doing, but there isn't "honoring" per se or the possibility of a bug. Removing the jumper breaks the path for the !WR_GATE signal.

Since jumper position is not monitored, you can tell it to write and it'll happily accept that, and nothing will be written. If the disk is actually getting written to, you have a hardware fault, most likely in the drive itself (as the only things after the jumper are the connector, cable, and drive).

[chadr]

Oh, well I see the problem now. This is a poorly designed feature and it will never work, and never has worked. Pin 24 tells the drive to not delete before write, but it does not prevent the write from still happening, and ruining a disk. I urge others to verify this for themselves before disks get clobbered accidentally.

[wohali]

No, that's incorrect. Pin 24 is the Write Gate pin on the Shugart bus. Invariably this is a hard stop within drives for writing.

Show me the schematic of any floppy drive and I will explain to you how the lack of the WGATE signal prevents writing to the diskette.

This was also a design goal of the hardware, and was validated during development. You do realise that @GeorgeRudolf developed the hardware and @keirf tested this before releasing the product, yet?

[GeorgeRudolf]

From the WD279x datasheet:

From the SA465 manual:

Here's a handy link to the SA400 manual in full, which you should probably consult in case any doubt remains:

https://deramp.com/downloads/mfe_archive/020-Disk%20Drives/Shugart/SA400/54102-2_SA400_OEM_Sep78.pdf

Your understanding of how a floppy works is fundamentally flawed. The drive mech has no concept of deleting or erasing. They only know read, or write. They don't know what's on the disk, they don't know what's being written, and they don't care, for there is no decoding logic built into the drive itself. As the name should have made obvious, WR_GATE... gates any writing. The head drive circuitry is not enabled unless it is asserted, i.e. driven low, which is made impossible on a normally-working drive with the jumper removed.