VidHD Manual Update – Floppy Disk Precautions

Today, I learned about two uncommon but risky situations with the VidHD card for the Apple II that can result in data loss. John Brooks and I discussed the details and I’ve edited and updated the manual on our website. In brief:

  1. Do not have an unprotected disk in your 5.25″ drive during power up, or data loss can result.
  2. Avoid accessing the VidHD Control Panel during disk writes, or data loss can result.

Most users do not encounter the first problem as they boot to a menu, or boot from a hard drive or other mass storage in the first six seconds, so the 5.25″ drive is not active during the VidHD DMA.  If the boot disk is write-protected, the startup DMA may cause an I/O error, but it will not write to the floppy.

For those booting an unprotected floppy disk, workarounds include:

1.  Press Ctrl-Reset at startup to turn off the drive, or 
2.  Hold Ctrl-Reset for six seconds while powering on the Apple II (delaying floppy boot until after VidHD DMA). 

Unfortunately, a firmware update will not fix this, as the problem is in VidHD’s bus bridge chip and/or inherent in doing DMA independently of the 6502 CPU, while the 6502 is doing critically-timed floppy access. John also said that it may be possible for data loss to occur on an Apple IIGS with a 3.5″ drive, but no problems have been reported to Blue Shift Inc.

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About the Author

Brian Wiser

Brian is an A.P.P.L.E. Board member and Managing Editor of Call-A.P.P.L.E.. He is a producer of books, films, games, and events, as well as an Apple consultant, historian and archivist. Brian designed, edited, and co-produced dozens of books including:  "Nibble Viewpoints: Business Insights From The Computing Revolution," "Cyber Jack: The Adventures of Robert Clardy and Synergistic Software," "Synergistic Software: The Early Games," "Graphically Speaking: Enhanced Edition," "What’s Where in the Apple: Enhanced Edition," and "The WOZPAK Special Edition: Steve Wozniak’s Apple-1 & Apple II Computers."  Brian also co-produced the retro iOS game "Structris." Brian was an extra in Joss Whedon’s movie “Serenity,” leading him to being a producer/director for the documentary film “Done The Impossible: The Fans’ Tale of Firefly & Serenity.” He brought some of the Firefly cast aboard his Browncoat Cruise convention and recruited several of the Firefly cast to appear in a film for charity. Brian speaks about his adventures at conventions around the country.