2 Jul
2008
2 Jul
'08
2:05 a.m.
Hi, all,
I'm in the middle of getting two bare PET boards working, one static, one
dynamic. I don't have great honking transformers lying around, so the
easiest way to power them is going to be a bench-top DC supply. One thing
that makes this a little easier is that I don't need to worry about cassette
motor power in this configuration - no tape drives and no tapes.
The static PET is easy - it has a few TO-220 7805s on it (which were removed
to get the very tall heat sinks off for easier packing and shipping). I
am not even sure I need +12VDC for that one - I don't think I do - just +5VDC
at a few amps (also made easier because it came with no ROMs and no SRAMs,
so I'm using one of Nicholas Welte's ROM/RAM boards that sits in the CPU
socket).
The dynamic PET, since it has soldered-in DRAMs, is a bit more complicated.
Unless I care to remove the DRAM and fit another ROM/RAM board for the SRAM
or adapt a 62256 in some other way, I need +12V and -5V for Vdd and Vbb on
the 4116 chips. My question (after all this background info) is... does
anyone have enough knowledge of the ICL7660 chip to give an opinion on how
well it would work for supplying -5VDC? Looking at datasheets, the max
draw I can find on Intel uP416s is 200uA @ -5VDC (along with all its other
needs). It looks like the ICL7660 will provide up to 10mA @ -5VDC, but at
some higher amount of inefficiency than at lower draws. 16x0.200 is 3.2mA,
well under the max draw of the ICL7660, so I think I'm OK, but I wanted to
ask other folks about this in case I'm overlooking some important detail.
I do have a real C= keyboard that made it before the last plane, and I
plan to build either a 74LS86 or 4066-based video adapter to drive a
standard monochrome security monitor (that I saved from being discarded
two years ago), so keyboard and video are taken care of (plus I have a
"C=Key" board that I probably have time to assemble to try using a
modern keyboard with). For a base PET, besides video and keyboard, the
only other issue is power, thus my question.
If the DRAM were socketed, I'd probably just pull it and use a 62256
in the ROM/RAM board and be done with it, but it might just be easier
to feed this board +5V and +12V and synthesize the -5V, unless it
turns out that I have a bad DRAM chip - then it's time to yank them
like a bad tooth (though I _think_ I know where I can find a few 4116
chips on a shelf here if it comes down to just one or two chips). If
I were home, it would be easy - I'd pull out a board from one of my PETs,
drop these boards in there at least for testing, then see about mounting
them in a box of some sort. Now, at least, the only C= stuff I have are
these boards and a few loose parts (like 65C02s and 65C22s).
One memory that's filtering up to the surface is that ISTR some
order-of-DC-powerup requirement for 4116s, like don't apply -5V
first or remove it last or some such. I plan to power the ICL7660
off of the +5V rail, but if there is a very specific order that
really matters, I might consider running it off the +12V rail
(with a 78L05 in-between) instead.
Thanks for any input or observations on the ICL7660 and/or 4116s.
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 2-Jul-2008 at 08:40 Z
South Pole Station
PSC 468 Box 400 Temp -83.7 F (-64.3 C) Windchill -114.0 F (-81.1 C)
APO AP 96598 Wind 6.1 kts Grid 58 Barometer 678.1 mb (10700 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
8:14 a.m.
Hi Ethan:
I use the 7660 all the time -- it needs two 100uF caps -- works
great! Can't draw a lot of current, but if the spec fits it is a great
solution.
There is a bit of switching noise (at about the switching freq of 5 to 10
KHz, IIRC), but it is usually not a problem.
There is some loss, which goes up as you load the device; ie: if you
drive it from +5.0V and load it lightly, you will get close to -5.0V, but
as you draw more current it will drop down to almost -4.0V. You can
compensate for this by driving it with about +6V instead (eg: a 78L05 with
a diode or two stuck in the ground lead).
Another was to go is to use a real switcher like an LM2674M-5.0, but
configured for -5 instead of +5 -- I use this chip all the time too for
both pos and neg 5V -- very efficient. Drive from unreg volage (eg: +12 to
+20 or so); you also need a 100uH inductor, a schottky diode, and a few
caps. Pricier, but can efficiently source up to an amp.
gil smith
Who is still looking for a Cromemco SCC board, BTW folks.
At 02:05 AM 7/2/2008, you wrote:
Hi, all,
I'm in the middle of getting two bare PET boards working, one static, one
dynamic. I don't have great honking transformers lying around, so the
easiest way to power them is going to be a bench-top DC supply. One thing
that makes this a little easier is that I don't need to worry about cassette
motor power in this configuration - no tape drives and no tapes.
The static PET is easy - it has a few TO-220 7805s on it (which were removed
to get the very tall heat sinks off for easier packing and shipping). I
am not even sure I need +12VDC for that one - I don't think I do - just +5VDC
at a few amps (also made easier because it came with no ROMs and no SRAMs,
so I'm using one of Nicholas Welte's ROM/RAM boards that sits in the CPU
socket).
The dynamic PET, since it has soldered-in DRAMs, is a bit more complicated.
Unless I care to remove the DRAM and fit another ROM/RAM board for the SRAM
or adapt a 62256 in some other way, I need +12V and -5V for Vdd and Vbb on
the 4116 chips. My question (after all this background info) is... does
anyone have enough knowledge of the ICL7660 chip to give an opinion on how
well it would work for supplying -5VDC? Looking at datasheets, the max
draw I can find on Intel uP416s is 200uA @ -5VDC (along with all its other
needs). It looks like the ICL7660 will provide up to 10mA @ -5VDC, but at
some higher amount of inefficiency than at lower draws. 16x0.200 is 3.2mA,
well under the max draw of the ICL7660, so I think I'm OK, but I wanted to
ask other folks about this in case I'm overlooking some important detail.
I do have a real C= keyboard that made it before the last plane, and I
plan to build either a 74LS86 or 4066-based video adapter to drive a
standard monochrome security monitor (that I saved from being discarded
two years ago), so keyboard and video are taken care of (plus I have a
"C=Key" board that I probably have time to assemble to try using a
modern keyboard with). For a base PET, besides video and keyboard, the
only other issue is power, thus my question.
If the DRAM were socketed, I'd probably just pull it and use a 62256
in the ROM/RAM board and be done with it, but it might just be easier
to feed this board +5V and +12V and synthesize the -5V, unless it
turns out that I have a bad DRAM chip - then it's time to yank them
like a bad tooth (though I _think_ I know where I can find a few 4116
chips on a shelf here if it comes down to just one or two chips). If
I were home, it would be easy - I'd pull out a board from one of my PETs,
drop these boards in there at least for testing, then see about mounting
them in a box of some sort. Now, at least, the only C= stuff I have are
these boards and a few loose parts (like 65C02s and 65C22s).
One memory that's filtering up to the surface is that ISTR some
order-of-DC-powerup requirement for 4116s, like don't apply -5V
first or remove it last or some such. I plan to power the ICL7660
off of the +5V rail, but if there is a very specific order that
really matters, I might consider running it off the +12V rail
(with a 78L05 in-between) instead.
Thanks for any input or observations on the ICL7660 and/or 4116s.
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 2-Jul-2008 at 08:40 Z
South Pole Station
PSC 468 Box 400 Temp -83.7 F (-64.3 C) Windchill -114.0 F (-81.1 C)
APO AP 96598 Wind 6.1 kts Grid 58 Barometer 678.1 mb (10700 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
Vaux Electronics, Inc.
480-354-5556
(fax: 480-354-5558)
www.vauxelectronics.com
8:50 a.m.
On Wed, Jul 02, 2008 at 08:14:32AM -0700, gil smith wrote:
Hi Ethan:
I use the 7660 all the time -- it needs two 100uF caps -- works
great! Can't draw a lot of current, but if the spec fits it is a great
solution.
Right. I've used them before, but mostly for negative LCD bias voltage
for HD44780-type LCDs - they don't need much current at all (I think I
was using 10uF caps, but 100uF is no problem to find).
There is a bit of switching noise (at about the
switching freq of 5 to 10
KHz, IIRC), but it is usually not a problem.
Probably won't be an issue for this application.
There is some loss, which goes up as you load the
device; ie: if you
drive it from +5.0V and load it lightly, you will get close to -5.0V, but
as you draw more current it will drop down to almost -4.0V.
Right. That was what I was a little concerned by - 16 DRAMs do add up
to some measurable current, even at 100-200uA each. What I wasn't sure
about is how quickly the ICL7660 drops off in a real application (vs a
nice clean curve on a spec sheet).
You can
compensate for this by driving it with about +6V instead (eg: a 78L05 with
a diode or two stuck in the ground lead).
Hmm... Hadn't thought of that trick; that might be handy if I need
a little boost.
Another was to go is to use a real switcher like an
LM2674M-5.0, but
configured for -5 instead of +5 -- I use this chip all the time too for
both pos and neg 5V -- very efficient. Drive from unreg volage (eg: +12 to
+20 or so); you also need a 100uH inductor, a schottky diode, and a few
caps. Pricier, but can efficiently source up to an amp.
I've seen mini-switchers like that in the past, 5 lead T-220 package,
IIRC, but I don't happen to have any handy, and I wouldn't be able to
get an order from Digikey for nearly 4 months in any case. I have
to use what's on hand.
Tonight, in preparation, I've been scraping off the broken wire stubs
and such from a previous owner's attempt to hack more memory onto it.
It looks like he mostly added external wires and only cut two or three
traces, but after I hit the old flux with some cleaner, the board should
look nearly good as new.
One thing I hope to find on funet/zimmers.net tomorrow when the 'net
comes up is a copy of the diag ROM at $9000 that's part of the offical
C= diagnostic dongle - I have one at home, a 40-pin clip for the CPU
that you clamp on, then press reset, then unclamp - inside is a '138
decoder and a 2716 EPROM - according to the docs, the clip forces the
CPU to execute at $9xxx not $Fxxx so it can pick up the ROM contents,
then it copies itself somewhere (zero page?) and performs some
rudimentary diagnostics. It's not as good as plugging in a Fluke 9010A,
but for a machine that mostly works (CPU, low mem, video, decode logic...)
it's a quick way to test things. Fortunately, there's room in the
RAM/ROM board for several sets of ROMs (it uses a 29F010 FLASH with
a DIP switch and a PAL), so even if I don't find the official C=
diagnostic pod code, I'm sure I can bang something out pretty quickly
and drop it into the FLASH instead of the official ROM code at $Fxxx.
If anyone has any comments on 4116 voltage "gotchas", I'd still love
to hear about them.
Thanks for the reply, Gil,
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 2-Jul-2008 at 15:30 Z
South Pole Station
PSC 468 Box 400 Temp -79.1 F (-61.7 C) Windchill -114.0 F (-81.1 C)
APO AP 96598 Wind 8.7 kts Grid 33 Barometer 680.4 mb (10613 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
10:24 a.m.
At 08:50 AM 7/2/2008, you wrote:
On Wed, Jul 02, 2008 at 08:14:32AM -0700, gil smith
wrote:
Yeah, it probably uses 10uF in the spec, but we standardize on a minimal
number of component values, and 100u works just fine, so less unique parts
to deal with for us -- whatever you have on hand should work for
you. Likewise, the 2674 specs a .01 uf feedback cap, but .1 works just fine.
I think one of the 7660's caps sees +/-5V switching for 10V total, IIRC, so
don't put a 6V part in there.
Also, I think the standard 7660 is good up to about 10V input. There is a
higher-volt part that I believe is a 7660S -- should work fine at 5 or 6V
input too, if that is what you scrounge up from your parts box.
Hi Ethan:
I use the 7660 all the time -- it needs two 100uF caps -- works
great! Can't draw a lot of current, but if the spec fits it is a great
solution.
Right. I've used them before, but mostly for negative LCD bias voltage
for HD44780-type LCDs - they don't need much current at all (I think I
was using 10uF caps, but 100uF is no problem to find). Another was to go is to use a real switcher like an
LM2674M-5.0, but
The 2674 is an 8-pin dip or soic. Nice part. Are you really at the South
Pole? 4 months to get stuff from digikey? Must be UPS (underwater parcel
service).
gil
Ethan Dicks, A-333-S Current South Pole Weather at 2-Jul-2008 at 15:30 Z
configured for -5 instead of +5 -- I use this
chip all the time too for
both pos and neg 5V -- very efficient. Drive from unreg volage (eg:
+12 to
+20 or so); you also need a 100uH inductor, a
schottky diode, and a few
caps. Pricier, but can efficiently source up to an amp.
I've seen mini-switchers like that in the past, 5 lead T-220 package,
IIRC, but I don't happen to have any handy, and I wouldn't be able to
get an order from Digikey for nearly 4 months in any case. I have
to use what's on hand. South Pole Station
PSC 468 Box 400 Temp -79.1 F (-61.7 C) Windchill -114.0 F (-81.1 C)
APO AP 96598 Wind 8.7 kts Grid 33 Barometer 680.4 mb (10613 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
Vaux Electronics, Inc.
480-354-5556
(fax: 480-354-5558)
www.vauxelectronics.com
3 Jul
3 Jul
1:55 p.m.
On Wed, Jul 02, 2008 at 10:24:22AM -0700, gil smith wrote:
The 2674 is an 8-pin dip or soic. Nice part.
I found some TNY267 parts - I know it's a switcher of some sort, but I'm
wondering how it relates to the 2674 you mentioned. The TNY267s I have
are 8-pin DIPs, minus pin 6 (not broken - just no leg where you'd normally
find pin 6). Ring any bells?
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 3-Jul-2008 at 20:50 Z
South Pole Station
PSC 468 Box 400 Temp -81.0 F (-62.8 C) Windchill -119.7 F (-84.3 C)
APO AP 96598 Wind 10.6 kts Grid 59 Barometer 680.6 mb (10606 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
2 Jul
2 Jul
10:41 a.m.
On Jul 2, 2008, at 11:50 AM, Ethan Dicks wrote:
DRAM chips tend to draw spikes of current during refresh, as those
little capacitors get charged. If you have adequate low-impedance
bypassing to supply those short-term demands, things should be fine
with the 7660. It's a fairly predictable and dependable chip.
There is some
loss, which goes up as you load the device; ie: if
you
drive it from +5.0V and load it lightly, you will get close to
-5.0V, but
as you draw more current it will drop down to almost -4.0V.
Right. That was what I was a little concerned by - 16 DRAMs do add up
to some measurable current, even at 100-200uA each. What I wasn't
sure
about is how quickly the ICL7660 drops off in a real application (vs a
nice clean curve on a spec sheet). I've seen mini-switchers like that in the past, 5
lead T-220 package,
IIRC, but I don't happen to have any handy, and I wouldn't be able to
get an order from Digikey for nearly 4 months in any case. I have
to use what's on hand.
Good heavens, one would think you're in Antarctica or something.
Oh, wait.. ;)
-Dave
--
Dave McGuire
Port Charlotte, FL
10:48 a.m.
On Wed, Jul 02, 2008 at 01:41:21PM -0400, Dave McGuire wrote:
Yes... ;) indeed.
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 2-Jul-2008 at 17:40 Z
South Pole Station
PSC 468 Box 400 Temp -81.9 F (-63.3 C) Windchill -121.1 F (-85.1 C)
APO AP 96598 Wind 10.8 kts Grid 46 Barometer 680.7 mb (10602 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
DRAM chips tend to draw spikes of current during
refresh, as those
little capacitors get charged.
Sure... I'm used to that with +5V-only chips like the 4164 and
up, but I don't have any design experience with the multi-voltage
parts, thus my caution.
If you have adequate low-impedance
bypassing to supply those short-term demands, things should be fine
with the 7660. It's a fairly predictable and dependable chip.
By low-impedance bypassing, you mean monolithic (not electrolytic) caps,
or do you mean something else?
... I
wouldn't be able to get an order from Digikey for nearly 4
months in any case. I have to use what's on hand.
Good heavens, one would think you're in Antarctica or something.
Oh, wait.. ;) 
6:13 p.m.
Ethan,
According to the Motorola datasheet - " All voltages referenced to Vss ( 0V)
and Vbb ( -5 Volts ) must be applied before and removed after other supply
voltages ".
What exacerbates things is that the current spikes from all the chips are
perfectly lined up during the RAS* cycle, but the biggest hit is on the Vdd
line ( +12 Volts ). If they don't already have a 0.1 uFd across each chip on
the Vdd I'd add one. I agree the 7660 should be okay on the - 5 Volts.
Also, don't think these will run at -63 C ( ha ha ha ).
Stay warm, Best regards, Steven
On Wed, Jul 02, 2008 at 01:41:21PM -0400, Dave McGuire
wrote:
Yes... ;) indeed.
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 2-Jul-2008 at
17:40 Z
DRAM chips tend to draw spikes of current
during refresh, as those
little capacitors get charged.
Sure... I'm used to that with +5V-only chips like the 4164 and
up, but I don't have any design experience with the multi-voltage
parts, thus my caution.
If you have adequate low-impedance
bypassing to supply those short-term demands, things should be fine
with the 7660. It's a fairly predictable and dependable chip.
By low-impedance bypassing, you mean monolithic (not electrolytic) caps,
or do you mean something else?
... I
wouldn't be able to get an order from Digikey for nearly 4
months in any case. I have to use what's on hand.
Good heavens, one would think you're in Antarctica or something.
Oh, wait.. ;) South Pole Station
PSC 468 Box 400 Temp -81.9 F (-63.3 C) Windchill -121.1 F (-85.1
C)
APO AP 96598 Wind 10.8 kts Grid 46
Barometer 680.7 mb (10602
ft)
Ethan.Dicks at usap.gov
http://penguincentral.com/penguincentral.html
7:31 p.m.
On Wednesday 02 July 2008 21:13, Scanning wrote:
According to the Motorola datasheet - " All
voltages referenced to Vss (
0V) and Vbb ( -5 Volts ) must be applied before and removed after other
supply voltages ".
Ah. I'd recalled that as being the case with some chips, but wasn't
remembering whether that applied to the 4116 in particular...
Nice to have it confirmed.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
8:54 p.m.
On Wed, Jul 02, 2008 at 06:13:22PM -0700, Scanning wrote:
Ethan,
According to the Motorola datasheet - " All voltages referenced to Vss ( 0V)
and Vbb ( -5 Volts ) must be applied before and removed after other supply
voltages ".
OK. I don't have _that_ 4116 datasheet to reference, but that does sound
familiar.
Looking carefully at the Commodore power supply schematics from zimmers.net,
I don't see anything that would bring up Vbb first or remove it last. To
all appearances, it's all three at once. I don't know of any voltage
priority in the Apple II, either (as an example of a contemporaneous
design to the dynamic PET), so presumably, "at the same time" suffices.
The unanswered (unanswerable?) question is then how close is close enough.
Given the replies, I think I'm going to try the ICL7660. It means that I
can run the board off a dual supply instead of trying to find other means.
There is a remote chance that it could blow all the 4116s on a semi-common
PET 3032 motherboard and I'll have to extract the chips - not a preferred
outcome, but it seems no more risky than the factory supply. The safest
alternative appears to be to remove the DRAM in the first place and run a
static chip on a ROM/RAM board, but that still involves a lot of work on
the board. What is clear is that providing +5V and +12V without covering
the -5V requirement is _not_ a reasonable option.
What exacerbates things is that the current spikes
from all the chips are
perfectly lined up during the RAS* cycle, but the biggest hit is on the Vdd
line ( +12 Volts ). If they don't already have a 0.1 uFd across each chip on
the Vdd I'd add one. I agree the 7660 should be okay on the - 5 Volts.
As originally manufactured by Commodore, the chips have 0.1 uF on both the
+12V and +5V rails. They are so notoriously cheap that I take it as proof
that they are required.
Also, don't think these will run at -63 C ( ha ha
ha ).
Fortunately, we have this nice warm indoor space - _I_ get to walk
~10 hrs/week outside, but the classic toys stay inside where it's nice
and toasty.
Thanks for all the advice,
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 3-Jul-2008 at 03:39 Z
South Pole Station
PSC 468 Box 400 Temp -83.2 F (-64.0 C) Windchill -121.6 F (-85.3 C)
APO AP 96598 Wind 10.1 kts Grid 45 Barometer 681.6 mb (10568 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
3 Jul
3 Jul
9:34 a.m.
On Wed, Jul 2, 2008 at 6:13 PM, Scanning
<steven.alan.canning at verizon.net> wrote:
Also, don't think these will run at -63 C ( ha ha
ha ).
You can get them rated -55C -- +125C. If the rest of your board works
at -63C, this probably will, too. So long as you don't have a lot of
money hanging on it. So Ethan can probably take this board outside
for a while.
We usually put thermal controls (heaters and thermostats) on a board
if we actually think it's going to see temperatures that low. But if
you want to go for simple and you don't have too many exposed parts
you can attach a small resistor to the TO-99 as a heater that you can
run off of an unregulated voltage.
9:57 a.m.
On Jul 2, 2008, at 1:48 PM, Ethan Dicks wrote:
I've only worked with 41256s design-wise. We used 8207 DRAM
controllers, which were great in terms of functionality, but good
heavens did we have problems with noisy power on those boards. I
never want to go through that again. Those refresh spikes had such
fast rise times (in ca. 1987 terms) that short, low-inductance paths
to the bypass capacitors within the DRAM array turned out to be very
important.
I just mean putting some decent bypassing electrically close to
the board; presumably there are already a reasonable number of bypass
capacitors in the DRAM array. Steven Canning said the supply that's
affected worst by refreshing is +12V...I didn't know that; if that's
the case then you shouldn't have to worry all that much about
bypassing -5V anyway.
Yes... ;) indeed.
:)
-Dave
--
Dave McGuire
Port Charlotte, FL
DRAM chips
tend to draw spikes of current during refresh, as those
little capacitors get charged.
Sure... I'm used to that with +5V-only chips like the 4164 and
up, but I don't have any design experience with the multi-voltage
parts, thus my caution. If you have
adequate low-impedance
bypassing to supply those short-term demands, things should be fine
with the 7660. It's a fairly predictable and dependable chip.
By low-impedance bypassing, you mean monolithic (not electrolytic)
caps,
or do you mean something else? ... I wouldn't be able to get an order from
Digikey for nearly 4
months in any case. I have to use what's on hand.
Good heavens, one would think you're in Antarctica or something.
Oh, wait.. ;)
10:40 a.m.
On Thu, Jul 03, 2008 at 12:57:43PM -0400, Dave McGuire wrote:
I've only worked with 41256s design-wise. We
used 8207 DRAM
controllers, which were great in terms of functionality, but good
heavens did we have problems with noisy power on those boards. I
never want to go through that again. Those refresh spikes had such
fast rise times (in ca. 1987 terms) that short, low-inductance paths
to the bypass capacitors within the DRAM array turned out to be very
important.
My design experience goes back only a tad farther - to 4164s and
74S409 DRAM controllers in a 128K array on the COMBOARD2 (circa
1983-1984). I didn't design it, but I was working with the
engineers when we had to figure out why it didn't work reliably
(we had to add 33Ohm resistors inline with the CAS/RAS lines
to dampen undershoot - a topic which has come up here in the
past once or twice).
I just mean putting some decent bypassing
electrically close to
the board; presumably there are already a reasonable number of bypass
capacitors in the DRAM array.
Yep. The PET board has two caps per DRAM chip (+12V and +5V) right
there next to the chips.
Steven Canning said the supply that's
affected worst by refreshing is +12V...I didn't know that; if that's
the case then you shouldn't have to worry all that much about
bypassing -5V anyway.
I didn't know about the larger noise on +12V either, but for this
particular application, I don't recall much else besides the RAM
array hanging off of the +12V line. As long as the noise doesn't
screw up refresh cycles, I don't think it will be a problem.
Cheers,
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 3-Jul-2008 at 17:20 Z
South Pole Station
PSC 468 Box 400 Temp -82.7 F (-63.7 C) Windchill -114.0 F (-81.1 C)
APO AP 96598 Wind 6.6 kts Grid 56 Barometer 681.1 mb (10587 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
2 Jul
2 Jul
9:46 a.m.
On Wednesday 02 July 2008 05:05, Ethan Dicks wrote:
The dynamic PET, since it has soldered-in DRAMs, is a
bit more complicated.
Unless I care to remove the DRAM and fit another ROM/RAM board for the SRAM
or adapt a 62256 in some other way, I need +12V and -5V for Vdd and Vbb on
the 4116 chips. My question (after all this background info) is... does
anyone have enough knowledge of the ICL7660 chip to give an opinion on how
well it would work for supplying -5VDC? Looking at datasheets, the max
draw I can find on Intel uP416s is 200uA @ -5VDC (along with all its other
needs). It looks like the ICL7660 will provide up to 10mA @ -5VDC, but at
some higher amount of inefficiency than at lower draws. 16x0.200 is 3.2mA,
well under the max draw of the ICL7660, so I think I'm OK, but I wanted to
ask other folks about this in case I'm overlooking some important detail.
That might be workable in terms of current draw, but that's not what I'd be
worried about there. I'm not real sure about the 4116 chips, but I seem to
recall that at least some of that early stuff that needed multiple supplies
needed to have that Vbb supply present _first_ and going away _last_. It's
getting it to come up first that I'd be worried about....
(Snip)
One memory that's filtering up to the surface is
that ISTR some
order-of-DC-powerup requirement for 4116s, like don't apply -5V
first or remove it last or some such. I plan to power the ICL7660
off of the +5V rail, but if there is a very specific order that
really matters, I might consider running it off the +12V rail
(with a 78L05 in-between) instead.
Just what I was thinking, above. But it's been so long that I really don't
remember in detail. It might not even have been the 4116 I was thinking of,
as there were a bunch of other chips that used multiple power supplies like
that, the 2708 coming to mind as well.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
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