18 Dec
2005
18 Dec
'05
7:44 p.m.
I dont own any. But according to a recent Circuit
Cellar article, early ics can be easy to implement in
a FPGA. Dont have the issue in front of me, but the
guy needed to mimic if you will a crt controller.
Therefore could the chips used in the early HPs (maybe
up to and including the 41 series?) be readily
emulated by an FPGA?
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19 Dec
19 Dec
2:26 a.m.
Chris M wrote:
I dont own any. But according to a recent Circuit
Cellar article, early ics can be easy to implement in
a FPGA. Dont have the issue in front of me, but the
guy needed to mimic if you will a crt controller.
Therefore could the chips used in the early HPs (maybe
up to and including the 41 series?) be readily
emulated by an FPGA?
CPLD's are a better part as most FPGA's require pre-load from rom.
Still you need the original hardware and docs to create a FPGA design.
Some designers played often some nasty tricks with hardware.
I think for example in the TRS 80 /I a 7400 with a defective unused
gate was used because it was cheaper than a working 7400.
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7:15 p.m.
I think for example in the TRS 80 /I a 7400 with a
defective unused
gate was used because it was cheaper than a working 7400.
I don't recall that, and I've worked on most TRS-80s, and read the
schematics. Of course there are unused gates that could be defecive.
BUT...
I remember a UK company called Bi-Pak. They bought up defective ICs,
tested them [1], and sold them. They did sell things like TTL quad-gate
packages with only 3 good gates. Problem was, as we all found, those 3
gates quickly failed in use.
[1] The tester was built from telephone relays and selectors. It ran at
about 1Hz. Plenty of chips passed that test and failed at more reasonable
speeds.... Don't ask how I found that out.
-tony
8:52 p.m.
New subject: Partially-bad chips; was: repairing early HP calcs
On 12/20/2005 at 12:15 AM ard at p850ug1.demon.co.uk wrote:
I remember a UK company called Bi-Pak. They bought up
defective ICs,
tested them [1], and sold them. They did sell things like TTL quad-gate
packages with only 3 good gates. Problem was, as we all found, those 3
gates quickly failed in use.
Back in the days when DRAM was precious, Intel had some "8Kx1" DRAMs that
were really "half good" 16K parts. You used the "-x" digit to
determine
which half to use. I don't know if these were in general circulation, but
the sales engineers were passing them out to customers working on designs.
I may still have one or two kicking around that I found actually had 16K
worth of usable bits, providing they weren't run too fast.
And there was bubble memory with a flaw map.
Aren't some (or all) high-density DRAMs now made with extra rows and colums
to improve yields?
Cheers,
Chuck
9 p.m.
New subject: Partially-bad chips; was: repairing early HP calcs
Chuck Guzis wrote:
Back in the days when DRAM was precious, Intel had
some "8Kx1" DRAMs that
were really "half good" 16K parts. You used the "-x" digit to
determine
which half to use.
I keep hearing rumours that this is done with modern hard disks too, and that
if one side of a platter tests bad then that platter will still get used in a
drive with that surface mapped out (e.g. company releases a 2-platter 40GB
drive, and a 30GB drive which is identical but with one failed surface)
Never confirmed that one, but I can see how it might make financial sense.
cheers
Jules
11:23 p.m.
New subject: Partially-bad chips; was: repairing early HP calcs
Chuck Guzis wrote:
On 12/20/2005 at 12:15 AM ard at p850ug1.demon.co.uk
wrote:
...
Back in the days when DRAM was precious, Intel had
some "8Kx1" DRAMs that
were really "half good" 16K parts. You used the "-x" digit to
determine
which half to use. I don't know if these were in general circulation, but
the sales engineers were passing them out to customers working on designs.
I may still have one or two kicking around that I found actually had 16K
worth of usable bits, providing they weren't run too fast.
And there was bubble memory with a flaw map.
Aren't some (or all) high-density DRAMs now made with extra rows and colums
to improve yields?
Cheers,
Chuck
I recall reading during one of the DRAM crunches (1986 or 1987) that tandy
bought their own $M tester to sort rejects that they bought cheap, doing the
same thing that you describe intel doing.
Redundancy in DRAM, row and column, has been in use for 20 years at least. At
the ASIC level, largish SRAMs typically also have redundant rows and columns
(largish meaning more than a few kbits).
It is also common knowledge that 3d chips, with their massive parallelism, also
practice large granularity logic reundancy, eg the perfect chips produce 16
pixels per clock and ones with defects produce 12 pixels per clock.
Sure, bubble memories had defect lists, but so do hard disks.
20 Dec
20 Dec
9:26 a.m.
New subject: Partially-bad chips; was: repairing early HP calcs
Chuck Guzis wrote:
Back in the days when DRAM was precious, Intel had
some "8Kx1" DRAMs that
were really "half good" 16K parts. You used the "-x" digit to
determine
which half to use. I don't know if these were in general circulation, but
the sales engineers were passing them out to customers working on designs.
I may still have one or two kicking around that I found actually had 16K
worth of usable bits, providing they weren't run too fast.
The ZX Spectrum actually has jumpers on the board to specify whether
you're using "top half bad" 32Kx1 or "bottom half bad", for the
upper
32k. Of course the ones that always went were the bloody awful 4116es.
Gordon
3:52 p.m.
New subject: Partially-bad chips; was: repairing early HP calcs
The ZX Spectrum actually has jumpers on the board to specify whether
you're using "top half bad" 32Kx1 or "bottom half bad", for the
upper
32k. Of course the ones that always went were the bloody awful 4116es.
There was nothing wrong with the 4116. The problem was that that chip is
known to fail if it loses the -5V bias supply (this is documented in the
data sheets, which, IIRC, give a supply line sequencing order), and
Sinclair (as usual) really cut corners with the -5V supply. It tended to
fail (or at least fail to start up), and the DRAMs failed
I must have well over 100 4116s in running machines here, and I think
I've had to replace exactly one of them.
-tony
1:35 p.m.
New subject: Partially-bad chips; was: repairing early HP calcs
Back in the days when DRAM was precious, Intel had
some "8Kx1" DRAMs that
were really "half good" 16K parts. You used the "-x" digit to
determine
There were certainly 32K*1 DRAMs that were half-good 64K chips. IIRC at
least one version of the 48K Spectrum used them, and there was a link on
the board to select which half would be used (obviously all 8 chips had
to be of the same type). I suspect the CoCo1 used them too.
-tony
19 Dec
19 Dec
3:18 a.m.
You should check out the "Discussion & Guest Areas" section of the
hpmuseum.org site.
- Evan
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Chris M
Sent: Sunday, December 18, 2005 7:44 PM
To: tech
Subject: repairing early HP calcs
I dont own any. But according to a recent Circuit Cellar article, early ics
can be easy to implement in a FPGA. Dont have the issue in front of me, but
the guy needed to mimic if you will a crt controller.
Therefore could the chips used in the early HPs (maybe up to and including
the 41 series?) be readily emulated by an FPGA?
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7:07 p.m.
I dont own any. But according to a recent Circuit
Cellar article, early ics can be easy to implement in
a FPGA. Dont have the issue in front of me, but the
guy needed to mimic if you will a crt controller.
Therefore could the chips used in the early HPs (maybe
up to and including the 41 series?) be readily
emulated by an FPGA?
There are 2 main problems...
1) The triival one is that the HP calculators did not use standard logic
levels. The Classics, Topcats and most of the Woodstocks (HP27 being the
exception) are PMOS, for example
2) The more serious problem is lack of documentation for the ICs. Eric
Smith knows more about this than me, having written emulators for these
machines, but in many cases data sheets plain don't exist, and when they
do, there are odd quirks. The NUT processor in the HP41 has a number of
bugs compared to the data sheet I have, for example.
And of coruse fitting an FPGA in place of an HP ROM/RAM chip (which would
cotnain, perhpas, 1K words of ROM and 16 56-bit 'registers' of RAM, with
an odd internface to the rest of the machine) which comes in an 8 pin DIL
package is another entertainment.
So yes, it can be done, but it is not trivial.
Shameless Plug Alert!
If you want to repair HP calculators, consider buying the HPCC Scheamtics
CD-ROM. It contains scehmatics for almost 70 calculators, small
computers, peripherals, etc. No, I don't get anything from the sales,
other than supporting HPCC.
-tony
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