| Attachment | Size |
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 DuoDisk_Pinout.pdf | 72.5 KB |
Hi,
While browsing various forums, I've noticed that people are having trouble connecting a DuoDisk to a Disk ][ card with two IDC20 connectors. Below is a diagram of such a cable (without the DB19 connectors). It's a direct connection from the DB25 to the two IDC20 connectors. Everything works and has been tested. The DB25 pinout is as described on the connector, but pay particular attention to the correct IDC20 pin assignment.
Sorry, Unitra but this SGS EPROM in place of P6 is an insult not only to many on this forum, but probably to Wozniak state machine, too. Thank you for you rocket science cable advice.
Can you explain this post?
The substitution of the state machine bipolar PROM with an EPROM was discussed previously (if only the search function worked). If I remember correctly, it works if the speed of the EPROM is faster than 150 ns or so.
Most hobbyists do not have the equipment required to program bipolar PROMs, so we see substitutions like this, even though it is not what Apple originally used. There were clone cards in he 1980s using EPROMs as well.
Sure, the topic of replacing PROM with EPROM is old and quite obvious to me, which is why I'm surprised. Especially since 2716 clone cards work fine. I have a PROM programmer, but only for 74S287, and I use it to burn Apple 1 and ACI chips.
https://www.applefritter.com/content/disk-ii-interface-card-prom-p6-replacement
Btw, this topic was about a simple pinout/connections, which may be useful to future searchers, because I personally, when looking for a ready-made one, did not find it.
Like I said, the broken search feature makes it harder to find the topics that previously discussed it. But here is one: https://www.applefritter.com/content/ibs-ap53-floppy-disk-controller-pcb-marked-ap41-why#comment-112142
where the timing is calculated, and it's close to the 150 ns I remembered.
On the topic, it's strange that the DuoDisk used a 25 pin cable to carry 19 signals. Does anyone know the history behind this? DB-19 is not a standard connector: was the original design (after the captive ribbon cables on the Disk II) using a DB-25, then later changed to DB-19 on the UniDisk after warranty issues from plugging DuoDisk cables into serial ports?
And thank you for testing the correspondence between the DB-25 and 20-pin ribbon Disk II cables.
probably because Apple III+ uses a 25 pin external drive connector. Probably.