Re: [avr-chat] Crystals (was ATmega32 @ 16MHz : fuse bits ??)

[Joerg Wunsch]

Dan <address@hidden> wrote:

> So the unprogrammed state was actually a 'closed' connection, thus
> creating a logic 1 as if you the switch was closed until you opened
> it.  This convention has remained intact over 30yrs year now.

I think it's not completely the same anymore.

While I can't seem to find any documentation on how to program an
74188 anymore (so I don't know whether they defaulted to 0 or 1 while
unprogrammed), I'm rather sure there used to be at least one EEPROM
that had an erased cell contents of 0.  ISTR this has been the 1702.
Very dreadful part, not only that it was quite common those days that
these NMOS chips needed +12 V and -9 V supply (plus the +5 V supply
needed to interface to TTL level), the programming algorithm involved
something like pulsing a number of pins (not just a single one) at
voltage levels like 30 or 40 V.

Starting with the 2708 (which still needed +12/+5/-5 V supply), the
EEPROM cell layout we are currently still using must have been formed,
only a single line needed to be pulsed with ~ 30 V (later on the pulse
driver went even internal, so the pulse only needed to have TTL level,
with Vpp being supplied constantly into one pin).

These cells are really quite a bit different from the diode matrix
cells of those ancient days.

-- 
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)