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Author Topic: G540 charge pump pin 16 is 2v instead of 5!  (Read 5055 times)

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Offline Tj256

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G540 charge pump pin 16 is 2v instead of 5!
« on: October 25, 2010, 11:16:25 PM »
It seems the G540 from GeckoDrive pulls down my nice 10 khz 5 volt signal on pin 16 down to 2 volts, and is not happy about it. Does anyone know if there is a solution to this? I think this is why many people try random parallel port cards until they find one that works. I'm hoping to find the reason behind this happening.

Thanks for any hints...

-Tj
Re: G540 charge pump pin 16 is 2v instead of 5!
« Reply #1 on: October 26, 2010, 01:10:48 AM »
Hi,

Have you read the GeckoDrive Initial setup guide that talks about putting the parallel port into EPP mode so that the chargepump will work?

http://www.geckodrive.com/upload/G540InitialSetup.pdf


Give it a go and report back.

Cheers,

Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com

Offline Tj256

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Re: G540 charge pump pin 16 is 2v instead of 5!
« Reply #2 on: October 26, 2010, 09:39:16 AM »
Peter,

I've got a "MosChip" based PCI card that doesn't provide such an option. The signal is indeed present, but for some reason the G540 loads it down.   I wonder why some signals like all the step/directions work fine, yet this one signal is loaded down and drops to 2 volts.

Before I change PCI cards, do you know why  EPP fixes things, and if the symptom is what I'm seeing? "Some functions may not work" seems vague. I've got an email into support so when I find out the answer I'll post here.

Thanks

-Tj

Offline Tj256

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Re: G540 charge pump pin 16 is 2v instead of 5!
« Reply #3 on: October 26, 2010, 09:58:54 AM »
I believe the answer is found at this website:  http://www.beyondlogic.org/spp/parallel.htm

"Note: Some control ports are not open collector, but have totem pole outputs. This is also the case with EPP and ECP Ports. Normally when you place a Parallel Port in ECP or EPP mode, the control port becomes totem pole outputs only.."

I think the behavior I'm seeing is the "open collector" output unique to a few pins, including pin 16. The PC is able to pull that pin low, and there's a pull-up resistor to bring it high. I even put my own pull-up on there just in case and that didn't work.

This tells me that the G540 loads that pin down too much, and the only fix is EPP mode or to put a buffer. We'll see what they say. If the answer is "EPP" then I will be surprised. I see so many people hitting this issue and are tossing perfectly good parallel port cards simply because of a missing buffer between pin 16 and the logic in the G540.

This also explains why when I "broke out" pin 16 to a breadboard and put a logic gate (basically made my own buffer) and THEN fed the G540 it worked. If this is indeed the problem, I hope GeckoDrive does the right thing and puts a buffer in rev3 of their product.

Hopefully there's a better fix forthcoming from the Gecko guys, but I'm going to make a small buffer circuit in the gender changer before I toss my parallel port card.

-Tj

Offline Tj256

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Re: G540 charge pump pin 16 is 2v instead of 5!
« Reply #4 on: October 26, 2010, 10:39:00 AM »
Ok, I can almost guarantee this *IS* the problem.

EPP can be enabled by toggling some bits in the parallel port control registers. In the case of an integrated card, the BIOS does this. For a PCI card, you either have to get a card that lets you toggle the port mode, or the controlling software (MachIII) needs to do it.

Why doesn't MachIII have an option to specify the I/O base of the control registers to enable EPP?  Why doesn't MachIII enable EPP mode itself? I know some PCI cards don't always put those registers at base+0x400, but a quick check in device manager would give you the upper registers' position.

I hope this doesn't come down to me having to write some stand alone program to do this, or wire up buffers. I think this problem is going to cause trouble with other functions like the VFD so I have to solve it.

With so many people having this trouble, I think integrating the EPP mode enable into MachIII would be the best solution, no?

So many of the problems I'm hitting seem to be hit by many other people. So imagine the pain saved by having Mach handle this stuff internally!

Offline Tj256

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Re: G540 charge pump pin 16 is 2v instead of 5!
« Reply #5 on: October 26, 2010, 11:23:21 AM »
Looks like the solution is to purchase the C26 buffer board from CNC4PC.COM

http://www.cnczone.com/forums/gecko_drives/95845-anybody_have_working_pci_parallel_card_g540_w_charge_pump_enabled-2.html

For the sake of everyone with PCI parallel port cards with no way of switching them to EPP mode... either MachIII needs an EPP enable feature, or GeckoDrive needs to buffer their inputs, or both! In the meantime, I'm going to buy this buffer board and move on.