Common A1200/4000 deaths, CIA chip

[Plaz]

I haven't repaired amigas as a service in several years, but while I did the surface mount CIA chips were a common cause of failure. Matter of fact, CIA chips have always been a failure point for Amigas, no matter the model.

Replacements for the older socket versions can be had by stripping an old dead A500 typically. Supplies for the surface mount versions in the 1200/4000 seem more scarce. I've read multiple post lately concerning or including references to dead 1200's and it had me thinking if many could be easily repaired with a new CIA.

With all the other work being done to emulate classics using FPGA technology, could it be possible to make an affordable replacement for a dead CIA? Or does enough documentation exist to make a new source of CIA's using another PCCL chip?

Plaz

[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.  

[Chain]

Cheapest way is using cia from another half dead board

[Plaz]

@amigaksi

That a nice cable to work around dead amiga floppies or a crippled CIA chip. But some CIA chips die so hard, they keep your amiga from booting at all.

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

[Plaz]

Cheapest way is using cia from another half dead board

Yes, but the point is to repair the half dead system.

Plaz

[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.

[alexh]

Have you tried a kernel parallel port driver (such as UserPort) to run your software under WindowsXP instead of Windows98?

I find your work very exciting. There are already several Floppy disk simulators in the works, one uses USB, the other Compact Flash cards and a MCU (no host)... all not on sale and looking expensive...

If your software could be made to run under WindowsXP (at the right speed) then I would definately buy a cable and the software (depending on the price).

If you used long ROUND floppy cables (aesthetically more pleasing) I'd be even more interested

Your solution should (with a little work) be able to run IPF (Software Preservation copy protected images) as well as ADF etc. by using their DLL. That would be VERY cool.

http://www.softpres.org/download

Move now... a bit of good marketting on the right channels and you could have a winner on your hands. You could even expand to C64, Spectrum etc.

[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.

[Bamiga2002]

What symptoms does a dodgy CIA-chip give on an A1200? Does it affect the floppy-connector in any way?

[Doobrey]

Bamiga2002 wrote:
What symptoms does a dodgy CIA-chip give on an A1200? Does it affect the floppy-connector in any way?

Depends on which of the 2 CIAs is flakey.

Floppy disk problems could be either chip,
U8 send all the control signals(motor, disk selects,head step + direction etc)
U7 reads it's status(write protect,disk change, ready etc.)

Other things that the CIAs affect...
Keyboard, joystick buttons+mouse button problems could be U7
Serial port is U8
Parallel port , data lines controlled by U7, control lines by U8

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.

[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.