FyberOptic
Guest
Sun Feb 07, 2010 10:39 am
I'm about to attempt building my own basic GAL programmer after doing
much reading on the web. But first, I've got me a few questions!
1.) For starters, why do GALs use all different programming
voltages? Is it based on the chip model? Is it based on the company
who made it? Both? Seems like it would have made more sense to just
design them for a standard voltage, much like how apparently 12v is
the standard to read their contents. Though maybe that'd have made
them more expensive, I dunno. Or maybe they did it on purpose so
you'd buy their programmers/software?
2.) Does going above the programming voltage by the fractions of
volts by which a programmer can increment actually kill the chip?
Cause they seem to be rather small increments.
3.) Why are the programming voltage and timings stored in the PES,
when from what I understand the PES is erased when you do a chip-
erase? I guess this means you have to make sure you read the PES out
first and save it, then write it back in after writing in your new
fuse settings, and hope nothing goes wrong in the meantime to lose
that configuration info.
4a.) Since I don't have a bench power supply, I'm going to have to
try to make do with something else. Would it be possible to use
something like a 7805 with a potentiometer on its ground, powered by
maybe 18-20v (whatever AC adapter I can find), to generate the
programming voltages?
4b.) Is it even safe to run an '05 much higher than its standard
output?
4c.) How does that affect its current output? And relatedly, am I
right in the assumption that the higher the output voltage (getting
closer to the input voltage), the cooler the '05 would be?
4d.) Would I need a resistor temporarily across the output of the
7805 to properly test its output voltage with a multimeter? Since I
assume the voltage might differ when connecting the meter directly
compared to when the '05 is connected to the chip and erasing. If
it's as sensitive to the voltage range as I've assumed, then I'd have
to make sure the voltage I generated was very accurate and all.
Forgive my latter questions if they sound dumb, but there's still much
that confuses me when it comes to "analog" electronics, as opposed to
digital circuits. But I'd appreciate any help anyone can offer!
Rich Webb
Guest
Sun Feb 07, 2010 3:56 pm
On Sat, 6 Feb 2010 23:39:48 -0800 (PST), FyberOptic
<fyberoptic_at_gmail.com> wrote:
Quote:
4a.) Since I don't have a bench power supply, I'm going to have to
try to make do with something else. Would it be possible to use
something like a 7805 with a potentiometer on its ground, powered by
maybe 18-20v (whatever AC adapter I can find), to generate the
programming voltages?
Use an LM317 or equivalent as your variable regulator. Dirt simple to
setup; see the data sheet. The voltage divider that sets the output
voltage also provides it a minimum load.
--
Rich Webb Norfolk, VA
FyberOptic
Guest
Sun Feb 07, 2010 7:39 pm
On Feb 7, 8:56 am, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
Quote:
Use an LM317 or equivalent as your variable regulator. Dirt simple to
setup; see the data sheet. The voltage divider that sets the output
voltage also provides it a minimum load.
Hiya, thanks for the response. Did ya get buried in the snow there
where you are in VA? Northeast TN here just ended up with a big pile
of rain.
I saw those LM317s and was wondering about them, but I asked about the
7805 in particular for a couple of reasons. First, because that's all
I have in parts at the moment without having to order anything. But
second, because I saw it being done. The schematic for an older
Willem programmer uses a 7805 and 7812, and both can have their
outputs changed based on diodes in series on their ground pin.
Jumpers can be set to bypass certain diode(s) to change the output
voltage. The jumpers on the 7812 for example can be configured to
output 12.5, 15, 21, and 25v. I thought this might be possible using
a pot or something instead of diodes. Though the way they're doing it
in series with the ground is what prompted my questions about load,
too, since I'm not sure how it affects the output to do it the way
they are.
Rich Webb
Guest
Sun Feb 07, 2010 8:21 pm
On Sun, 7 Feb 2010 08:39:32 -0800 (PST), FyberOptic
<fyberoptic_at_gmail.com> wrote:
Quote:
On Feb 7, 8:56 am, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
Use an LM317 or equivalent as your variable regulator. Dirt simple to
setup; see the data sheet. The voltage divider that sets the output
voltage also provides it a minimum load.
Hiya, thanks for the response. Did ya get buried in the snow there
where you are in VA? Northeast TN here just ended up with a big pile
of rain.
Just enough to cover the ground, this time.
Quote:
I saw those LM317s and was wondering about them, but I asked about the
7805 in particular for a couple of reasons. First, because that's all
I have in parts at the moment without having to order anything. But
second, because I saw it being done. The schematic for an older
Willem programmer uses a 7805 and 7812, and both can have their
outputs changed based on diodes in series on their ground pin.
Jumpers can be set to bypass certain diode(s) to change the output
voltage. The jumpers on the 7812 for example can be configured to
output 12.5, 15, 21, and 25v. I thought this might be possible using
a pot or something instead of diodes. Though the way they're doing it
in series with the ground is what prompted my questions about load,
too, since I'm not sure how it affects the output to do it the way
they are.
A quick look at the LM78xx datasheets shows that most of the adjustable
examples use a unity gain opamp to isolate the ground (which becomes the
ADJ pin) from the voltage divider that sets the reference voltage. E.g.
<http://www.fairchildsemi.com/ds/LM%2FLM7805.pdf>
Nothing wrong -- and probably much to be gained -- from trying both ways
and comparing the operating characteristics.
--
Rich Webb Norfolk, VA
Peter Bennett
Guest
Sun Feb 07, 2010 9:13 pm
On Sun, 7 Feb 2010 08:39:32 -0800 (PST), FyberOptic
<fyberoptic_at_gmail.com> wrote:
Quote:
On Feb 7, 8:56 am, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
Use an LM317 or equivalent as your variable regulator. Dirt simple to
setup; see the data sheet. The voltage divider that sets the output
voltage also provides it a minimum load.
Hiya, thanks for the response. Did ya get buried in the snow there
where you are in VA? Northeast TN here just ended up with a big pile
of rain.
I saw those LM317s and was wondering about them, but I asked about the
7805 in particular for a couple of reasons. First, because that's all
I have in parts at the moment without having to order anything. But
second, because I saw it being done. The schematic for an older
Willem programmer uses a 7805 and 7812, and both can have their
outputs changed based on diodes in series on their ground pin.
Jumpers can be set to bypass certain diode(s) to change the output
voltage. The jumpers on the 7812 for example can be configured to
output 12.5, 15, 21, and 25v. I thought this might be possible using
a pot or something instead of diodes. Though the way they're doing it
in series with the ground is what prompted my questions about load,
too, since I'm not sure how it affects the output to do it the way
they are.
Yes, you can use the 78xx series of regulators to produce higher
output voltages. Use the same circuit as for the LM317, but if you
are using a 7805, use 5 volts where the LM317 formula uses 1.2 volts -
the LM317 is really a 1.2 volt regulator optimised for this "lifted
ground" use.
When using the 78xx series this way, you should check on the current
through the ground pin, as it will affect the output voltage if it
varies significantly with load current.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info:
http://vancouver-webpages.com/peter
Vancouver Power Squadron:
http://vancouver.powersquadron.ca
Peter Bennett
Guest
Sun Feb 07, 2010 9:17 pm
On Sat, 6 Feb 2010 23:39:48 -0800 (PST), FyberOptic
<fyberoptic_at_gmail.com> wrote:
Quote:
4d.) Would I need a resistor temporarily across the output of the
7805 to properly test its output voltage with a multimeter? Since I
assume the voltage might differ when connecting the meter directly
compared to when the '05 is connected to the chip and erasing. If
it's as sensitive to the voltage range as I've assumed, then I'd have
to make sure the voltage I generated was very accurate and all.
Not in my experience. The 78xx family of regulators do have a minimum
load current spec, below which the device is not guaranteed to meet
its specs. However, I have always found that, with no load other than
my meter, the output voltage is close enough to the spec for me.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info:
http://vancouver-webpages.com/peter
Vancouver Power Squadron:
http://vancouver.powersquadron.ca
Mark Zenier
Guest
Sun Feb 07, 2010 10:39 pm
In article <caae4eb7-a3ce-44e8-94c8-9460722612d6_at_l26g2000yqd.googlegroups.com>,
FyberOptic <fyberoptic_at_gmail.com> wrote:
Quote:
I'm about to attempt building my own basic GAL programmer after doing
much reading on the web. But first, I've got me a few questions!
1.) For starters, why do GALs use all different programming
voltages? Is it based on the chip model? Is it based on the company
who made it? Both? Seems like it would have made more sense to just
design them for a standard voltage, much like how apparently 12v is
the standard to read their contents. Though maybe that'd have made
them more expensive, I dunno. Or maybe they did it on purpose so
you'd buy their programmers/software?
(I speculate): The main design goal is to get the logic array as fast
as possible, so they would design the chip towards that goal, and then
characterize the programming algorithm to give the best results for
speed and storage reliabilty. Toss in the use of different semicondutor
processes as time goes on, and thing get very variable.
PLD manufacters outsourced the manufacturer of device programmers
(and the customer support costs that go along with that).
Quote:
2.) Does going above the programming voltage by the fractions of
volts by which a programmer can increment actually kill the chip?
Cause they seem to be rather small increments.
My guess is that the numbers came from what gave the best programming
yield and aren't that critial.
Quote:
3.) Why are the programming voltage and timings stored in the PES,
when from what I understand the PES is erased when you do a chip-
erase? I guess this means you have to make sure you read the PES out
first and save it, then write it back in after writing in your new
fuse settings, and hope nothing goes wrong in the meantime to lose
that configuration info.
As I remember, the PES erase was seperate, but it's been over 15
years since I was hacking around with this stuff.
Mark Zenier mzenier_at_eskimo.com
Googleproofaddress(account:mzenier provider:eskimo domain:com)
