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Whats the purpose of this jumper on this ieee-488 adapter?

VERAULT

VERAULT

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Im trying to do some testing with all of my commodore ieee-4888 drives and Its been a long time since I used them. First question. Whats the purpose of the 3 pin jumper on the adapter? "IFC" Is stenciled above them.
IMG_20240415_123158.jpg
 
The system controller is the only device allowed to drive IFC (interface clear)
I expect the jumper is set to allow the PET to be system controller.
 
So i booted up my other PET. And It seems the issue is my IEEE-488 Bus on one of my pets is no longer working. Swapping the socketed ic's resulted in no change. After doing some reading I think the issue is the MC3446N Bus Tranceivers. I put in an order for some.
 
VERAULT said:
So it will be fine with no jumper than?
Click to expand...

If you flip that thing over can you trace what the jumper disconnects? It's possible you have to have it set by default and no jumper disconnects it? Of course, off the top of my head I have no idea if the PET drives require it connected or not.
 
(wild guess) As it's a three-pin jumperheader, there's a chance that (for example) pin 1 is GND, pin 3 is some "source" signal pin, and pin 2 is IFC. Bridging pins 1-2 pulls IFC to ground, bridging pins 2-3 makes it do whatever the source signal pin is doing, and running with no jumper lets one of the computers drive IFC.

It could be a different configuration, but my point is that "no jumper" could select one of up to three options that this jumperheader makes available. But the actual traces will tell the real story.

(ETA: got too enthusiastic about the word "jumper", probably because it's a chilly April evening!)
 
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VERAULT said:
So i booted up my other PET. And It seems the issue is my IEEE-488 Bus on one of my pets is no longer working. Swapping the socketed ic's resulted in no change. After doing some reading I think the issue is the MC3446N Bus Tranceivers. I put in an order for some.
Click to expand...
Where did you put in the order ?

Unfortunately there are a few fakes of these now. But I know the source for genuine original vintage parts, if you get stuck.
 
There is a test program for the IEEE-488 port on the PET written in BASIC. Type it in and RUN to test the port (without anything connected to the bus of course).

This code was in a book, and it is available online as a PDF.

Unfortunately, I am on a business trip this week, otherwise I would reach onto my bookshelf and post the details for you.

Perhaps someone else could oblige?

Dave
 
Hugo Holden said:
Where did you put in the order ?

Unfortunately there are a few fakes of these now. But I know the source for genuine original vintage parts, if you get stuck.
Click to expand...
You know I was trying to find an email to tell me where.. But I just couldn't find one. I bought it a few years back and I am not sure where.
 
So here is where those jumper pins go on the adapter: Top Pin marked blue goes to pin 9 on ieee-488 female connector. Middle pin marked Red goes to pin 9 on PET ieee-488 card edge connector. Bottom pin seems to go nowhere at all.

IMG_20240416_094944.jpg
ieee488female.png
IMG_20240416_094634.jpg
 
Pin 9 is IFC, like it says on the tin. So no jumper there means IFC is not connected.

Looking at the schematics for the Commodore 4040 and 8050 disk drives it doesn't look like they have anything attached to that line, so I would presume for running a disk drive it wouldn't matter if you had that jumpered or not, but there's probably no harm in trying it either way.
 
It inverts reset so when the PET gets a reset, the interface clear line is pulled and all devices no matter what they are doing immediately let go of the line and await further commands (if they follow the IEEE-488 spec).
 
Anyone know if there is a seller in the states for these Adaptors? I swear I had more than one but after alot of searching this is the only one I have.
 
Gary C said:
It inverts reset so when the PET gets a reset, the interface clear line is pulled and all devices no matter what they are doing immediately let go of the line and await further commands (if they follow the IEEE-488 spec).
Click to expand...
Gary,
That is correct, but note that the /Reset signal is not inverted (the 7417 is a non-inverting buffer). The /IFC is also a LOW active signal.
 
Eudimorphodon said:
Looking at the schematics for the Commodore 4040 and 8050 disk drives it doesn't look like they have anything attached to that line, so ...
Click to expand...
Hi Eudimorphodon,
It's a bit hidden on the lower right of the sheet 1 schematic for the 4040, but /IFC is connected to the 555 timer circuit and will reset the 4040. Whenever I reset the PET, it does recycle the 4040.
So the jumper should be left in place to bridge the /IFC signal to the IEEE connector.

I only wonder why it's an option not to connect it? If one wanted to use another computer on the 488 bus as the controller and the PET as an instrument, then you could leave this connection open, but as all the canned routines in the PET BASIC are for it to act as a controller, one would need to write an assembly language program for the PET to allow it to respond properly to incoming commands.
-dave_m
 
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