Alt-BEAM Archive
Message #09870
To: beam@sgiblab.sgi.com
From: Bruce Robinson Bruce_Robinson@telus.net
Date: Mon, 07 Feb 2000 12:49:12 -0800
Subject: [alt-beam] Re: 74HCI4 Microcore Question
Geoff Waters wrote:
>
> PS: Know of ant free PCB design software i can dowload, ...
Express PCB has free downloadable software. They provide it free because
they expect you will order the finished circuit board from them.
However, a few BEAMers report that they can print the finished design
with a little effort. You'll find the download link at
http://www.expresspcb.com/
About 4.5 Mb last I looked.
> ... is the Microcore chip 74C14, 74HC14, 74HCT14, so many people
> have so many different versions.
Hi again, Andrew.
These chip designations are fairly generic between different
manufacturers. The different letters following the '74' indicate the
chip family (basically, the technology used to manufacture the chip.
For a microcore you want a CMOS chip with static protection (see
footnote). All the devices you mention are CMOS devices; the HC and HCT
families have the necessary static protection; I suspect, but don't know
for certain, that the C family does as well.
74C14 = CMOS Hex Schmitt inverter.
74HC14 = High speed CMOS Hex Schmitt inverter.
74HCT14 = High speed CMOS Hex Schmitt inverter with
TTL compatible inputs.
"High speed" is not particularly relevant to most BEAM applications. The
chief differences between the HC and HCT families is the HCT can supply
higher output current, and has a maximum supply voltage fo 5.5 V (versus
6.0 V for the HC).
Footnote: why on earth should static protection matter? Wilf tipped me
off on this one. If you analyze the electron flow in a neuron, viewing
it as simply an inverter, a resistor, and a capacitor, it SHOULDN'T
WORK!! It needs something else -- a diode. As it happens, the CMOS
devices, being very susceptible to static discharges, have internal
voltage limiting diodes on all their inputs. So by coincidence, it is
the static protection on CMOS chips that allows the microcore to work
properly with only two other devices per neuron. I suppose in theory
that you could use LS, ALS, and other TTL chips in a microcore by
providing external diodes. Don't know why you would want to, though.
There's no price advantage and the chips draw way more current.
Regards,
Bruce
9871 Mon, 7 Feb 2000 17:34:02 EST [alt-beam] Re: Tutorial beam@sgiblab.sgi.com BowfinGar1@aol.com I think you should make a two motor walker tutorial. I have seen many on
photovores but I haven't seen many on walkers. I think you would ge helping
out many hobbiest ( such as my self ) if you made a walker tutorial.
BowfinGar1@aol.com
( Mark )
9872 Mon, 07 Feb 2000 17:09:07 -0600 [alt-beam] Plastic Muscles? beam@sgiblab.sgi.com, stamps@parallaxinc.com bill_r@inetnebr.com (Bill Richman) Move over, memory metal!
http://www.msnbc.com/news/365892.asp?0m=N21B
Bill Richman
incolor.inetnebr.com/bill_r
(Home of the COSMAC Elf
microcomputer simulator!)
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