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SIO2PC USB daisy chained to 1050 - ISSUES


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So I ended up building my own SIO2PC USB using cheap ebay FTDI board. Works beautifully, but when I attempt to daisy chain to my 1050 floppy, the floppy drive seems to go into limp mode and will no longer work until I unplug it, let it sit for a bit, power it on/off a few times with the SIO plug out, then it works fine.


Am I doing something wrong? Is there something I neglected to connect?


Pictures of the build process: (still need to cover cables between project box and SIO plug)






FTDI board is now connected to lower portion of project box with double sided foam tape and the female micro-USB extends out a small opening I created.


NOTE: The orange wire in the SIO plug is not connected to anything. This was a parts plug I pulled from a ATARI 410. Swapped one wire to PIN 7.


I have the following set-up:


PIN 3 ==> TX

PIN 4 ==> GND

PIN 5 ==> RX

PIN 7 ==> CTS


Side note: I used a standard RS232 (no hand shaking capability) cable prior to this and it did the same thing.

Edited by NISMOPC
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have you set your 1050 as Drive 2 and make sure your emulator has that drive set up as free?

This might be my issue. I tried setting 1050 as Drive 2, but same issue. I was reading where you have to set the SIO2PC to Drive 1 within the PC software and mount a DOS image to first virtual drive. Am I on the right track? First time attempting the daisy. Actually, first time dabbling in Atari since I was in my pre-teens with my 800XL.

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I seem to recall somewhere that using an SIO2xxxx device along with a real drive requires a diode or something like that between a pair of lines on the device. Otherwise it effectively takes control of the SIO bus and the real drive won’t work. A search of the forum may turn up more information.

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Probably best to verify the thing's not electrically screwing around with the serial chain.


Plug 1050 in as D1: and try the SIO2PC device hanging off the drive. Try connected to the PC and not connected, and do so without any host emulation software going.

If that's good, try with a blank image on the PC host as D2: and see if you can boot a real Dos floppy and copy it from 1050 to an image on PC.


I've not heard of diodes, whatever. When I built my first one (RS232 type) there was mention of decoupling capacitor, not even sure I retained it as I had to do some fiddling to get it to work.

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Actually, the diode is needed for all clone FTDI SIO2PC boards.


I made several home brew SIO2PC, 10502PC and SIO2PC/10502PC Dual-USB devices


See this link: Cheap but Effective.

Especially, posts #16 and 30



I actually based most of my build off of that thread. I "assumed" only the blue board you used needed it, not the red. I'll get the diode...



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The Atari SIO bus is what's known as 'open collector' on the RX line (device --> Atari computer). This allows multiple devices to use the line without interfering with each other. The diode is a kludge that converts a normal push-pull signal into an open collector signal, and is generally good enough in this case. Without the diode, the FTDI can drive the line high and, if it drives hard enough, prevent the real disk drive from communicating.

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Actually, the diode is needed for all clone FTDI SIO2PC boards.


I received 10 1N914 diode's in the mail today. Pulled one out, soldered inline between TX and PIN3. Set the 1050 as D1 and left the D1 slot open on AspeQt. 1050 drive booted up as normal.


I am tired and going to bed, but will be trying to understand the loading of a blank image then copying DOS image over on ApesQt tomorrow. Thanks again Madi and Rybags.

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