Common A1200/4000 deaths, CIA chip

[amigaksi]

In my experiments with the Floppy drive simulator with Amiga 1200 and Amiga 4000:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=ADME:L:LCA:US:11&item=320091931315

I found that the CIA chip behaves differently on these two machines; I can't seem to program the SIDE, DIR, and STEP pins on the CIA chips on the Amiga 4000 for input mode while I can do that on the Amiga 1200.  

[amigaksi]

You need at least the RDY, TK0, DKRD, SEL0, and SIDE signals working to at least to get the boot block loaded.  Then in the boot block you can reprogram the floppy controller into a parallel port and do asynchronous transfers and thus you won't have to trash the entire Amiga motherboard (assuming you don't know how to solder/desolder the CIA chips).  The Amiga Floppy Servers one of which is also on auction:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=ADME:L:LCA:US:11&item=320091938536

uploads 2 Gigabytes of multimedia data using this approach along with simulating floppies in synchronous mode.  (Using the synchronous floppy protocol was too slow for multimedia applications).

The multimedia application would not run on A4000 because it would not let me reprogram SIDE, DIR, nor STEP into input mode.  It runs fine on the A1200.  I had to rewrite the boot code for the A4000 to use other pins.

[amigaksi]

It will run under Windows 2000/XP but you need higher bandwidth parallel port since Windows 2000/XP slow down the transfer rate.  It comes with its own driver for these Windows platforms.  Windows '98 is faster than these two Windows OS.  The DELL computer (Amiga Floppy server) on auction:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=ADME:L:LCA:US:11&item=320091938536

barely meets the throughput required for simulating floppy disk drives.  If I install Windows 2000/XP on the Dell, the transfer rate slows down to 850 Kilobytes/second versus about 950 Kilobytes/second under Windows '98SE.  Does Userport driver make the transfer rate under Windows 2000/XP same as Windows '98SE?

It should work with all ADF files since they are just uncompressed sector dumps of the disk.  I am not familiar with the other disk formats that you mentioned.

[amigaksi]

About ROUND cables, the manufacturer would only do ribbon cables since I was using the internal floppy connector of the Amiga not the 23-pin external floppy connector.  The SEL0 signal required for booting on most Amigas is only available on the internal floppy connector.  The floppy simulator cable for the Atari 800/XL/XE series is a round cable since their floppy drives were always external.  The cable that's on auction:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=ADME:L:LCA:US:11&item=320091931315

 is for the Amiga series of computers.  The cable for the Atari computers is on the website: http://www.krishnasoft.com/sps.htm.  That cable for the Atari also does Amiga keyboard, Amiga mouse, and Amiga joystick simulation as well using a second parallel port.  That cable also works with any parallel port since the bandwidth does not have to be that high for mouse, keyboard, and joystick simulation.  

[amigaksi]

If you (or anyone) is interested in the Atari version, I'll substitute the cable in the auction with the right one.  The Atari version does read and write; it's a complete floppy replacement.  Although I did get the read and write mode working with Amiga floppy simulation under MSDOS, I have only got read mode working in general with Windows 98/ME/2000/XP.  

This is not a big problem for a few reasons:
(1) many games don't write to the disk and some that I tested that do write to the disk got fooled into thinking that the write was successful (i.e. Vyper).  

(2) there is a 680x0 Assembler on the PC end so you can write the code on the PC side and save it on your PC and have it run on the Amiga.

(3) you can chain the simulated disk drive with a real disk drive.  So you can copy an image disk to a real disk using a disk copy program on the Amiga.  So if you ran a word processor from a simulated disk, you can save the document to a real disk in a real disk drive.

[amigaksi]

>That's interesting. I would think they would be identical. >Some one with the right documentation could probably >answer this. Dave Haynie are you there?

>Plaz

The CIA chip behavior is different even on some Amiga 1000s and even after swapping the 8520 chips from an Amiga 500 so it seems that circuitry external to the CIA chip is preventing some of the output pins from being programmed for input mode (since on the Amiga 500/1200/2000/2500/3000 the 8520 can be programmed for input and output).

Here's another floppy server I just put together for those who missed it last time:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320112219800

And if you just want the floppy simulator cable:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320112223017

I wrote a quick version of Amiga 1000 Kickstart that uses only 1 Kilobyte of memory and just allows for uploading files from MPDOS on the PC end so using the floppy simulator cable, you can use 767KB of memory on the 512KB Amiga 1000 (assuming you don't call Kickstart functions).  Also, makes booting up quicker as you don't have to go through a two step (two disk) boot up process.  Of course, the extra RAM is fast RAM not chip RAM and would be at location $F80000..$FBFFFF not consecutive with the Chip RAM.  That preliminary version of KS is included with the floppy simulator cable.

[amigaksi]

Quote:

    I found that the CIA chip behaves differently on these two machines; I can't seem to program the SIDE, DIR, and STEP pins on the CIA chips on the Amiga 4000 for input mode while I can do that on the Amiga 1200.



That's interesting. I would think they would be identical. Some one with the right documentation could probably answer this. Dave Haynie are you there?

Plaz

I finally got around to tracing that problem.  It's the 74125A chip on the motherboard that cripples the bidirectional capability of the 8520 CIA chip.  The DIR, STEP, and SIDE signals go through the 74125A chip and makes the signals output only.  The SEL0/SEL1 signals do not go through the 74125A chip.  The Amiga 1000 has a similar problem using a different chip 7407.  I'll post the details once I modify another Amiga 1000 to make it bidirectional (so I know it's consistent with other Amiga 1000s).  The logic equation for 7407 states Y=A but A!=Y so the logic being non-commutative makes the 8520 uni-directional.

[amigaksi]

On the A500, A2000, A3000, and A1200, the signals I was referring to are bi-directional already since they are not going through the 74125A like they are in an A4000.  On the A1000, they are going through the 7407 which makes them uni-directional.  Regardless, they should not affect the normal functionality of a floppy drive since the floppy drive only uses them for input (output on the Amiga end).  However, in reference to the floppy simulator:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320148543065

I wanted to support normal floppy functionality as well as bi-directional parallel communications for faster transfers once the system boots so I was trying to trace down why I was unable to do bi-directional parallel transfers on the A4000 and A1000.  

One thing I did notice is that floppy failure is not necessarily the CIA fault since the 7407 or 74125A or some other supplementary chip could be faulty and the CIA chips could be just fine.

[amigaksi]

>Keep in mind that faults elsewhere in the Amiga could cause >the same problems, such as broken traces, shorts or faulty >components between the CIA and the floppy,parallel and serial >ports.

Right.  And also the other components can cause failure of the CIA chips.  I have seen a bad 7408 chip pop the top off a 8520 chip in an A1000 (and I could see the transistor grid behind the black cover).  [The 7408 is the invertor chip with various timing signals.]

Anyway, you can modify the Amiga 1000 7407 to make the CIA bidirectional just like it is on the Amiga 500.  The way I did it was to disconnect the +5V (VCC) pin.  Connect the A and Y signals together for the DIR, SIDE, and STEP signals.  This effectively makes these signals bypass the 7407.  The floppy dirve and floppy simulation still work and the signals can now be used bi-directionally.

Addendum: The above proves also that if you have a faulty 7407 chip on the Amiga 1000, you don't have to replace it.  You can just bypass it by making the signals go through directly from the 8520 to the floppy connectors using modifications similar to the ones I made.

[amigaksi]

Disconnect the keyboard and see if it boots.  I have an Amiga 500 with the keyboard where the RESET is jammed so you just get a white screen as if someone continuously held down the reset key.  If you are technically inclined and find it's the keyboard, you could use the simulated keyboard with it by modifying the A500 or A2000 keyboard cable available here:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320148538163

It's helpful for diagnosing even if you decide not to always use it.

[amigaksi]

...
>Years ago I got hold of a couple of A1200 boards that had had >their CIAs removed, and I found the pinouts and soldered up >the chips from an A500 onto the 1200 board.
>
>It looked like it was going to boot, but then the power LED >blinked some kind of error code and it didn't go any >further... Either the boards had some other problem (likely) >or something was wrong with the transplant...

I never tried that but there is some difference in the frequency tolerance between the Paula/8520 (CIA) combo floppy controller on the Amiga 1200 verses the Amiga 500.  I was able to run a floppy simulator using only 950KB/second parallel port on the Amiga 500 and Amiga 1000/2000/3000, but on the Amiga 1200 I needed a parallel port on the PC that was much closer to 1 Megabytes/second.