On Fri, Apr 30, 2004 at 01:07:51PM -0400, John Allain wrote:
There's a big Toshiba TMP80C49P that looks like a
MCU to me. Some minor things like Motorola SN74LS(05N,138N).
Nearest the SIO port are just a few resistors and two
transistors. At least one leg of the SIO goes directly to
the toshiba. Looks non-RS232 then... Whatsit 5V instead of 15?
On one of my Futaba VFDs (inside a "Pole Display", just like the kind
you see at WalMart - 20x2 in a rectangular box on top of a 1-1/2" pipe),
has a _really_ simple RS-232 level shifter on a small PCB that sits on
the back of the VFD itself... it's no more than two resistors and a
transistor. The Futaba display wants TTL serial (+5V/GND), but the
Pole Display spec is (over a 6-pin DIN identical to what C= used for
their IEC bus) RS-232 serial in and about 7-9VAC (which is rectified
and passed through a 7805 on that same little daughterboard).
"Official" RS-232 is anywhere from +/-3V up to +/-15V (check the
output of a laptop sometime - it's nowhere close to +/-15V). TTL
never goes negative. Check to see that your "direct leg" isn't your
ground. Those transistors and resistors could easily be your level
shifters. Worst case, though, if you are only sending to the
device and don't have to read from it, is to send it TTL levels
(buffered of course, to protect your sending device), and it may
well be able to receive. You'd need to know the character protocol
to be sure the device understood you, though.
The 80C49 _was_ commonly used for keyboards, but is just a general-
purpose Intel microcontroller. We used one in a product that was
never very successful (I think we sold 3!) called the "ComBox". I
still have several dozen sets of parts to assemble, if there were
ever a demand - an 8049 between two SLIC (Subscriber Line Integrated
Circuits), simulating the CO between two phones. Depending on the
number you dialed, you could get a half-connection, a full connection,
a connection without ring, or any one of a number of busy signals.
We used it for developing auto-dial software for, what was that
standard, V.25?, the kind that came out after 801ACUs. I didn't
write the code for our 8049 (the hardware engineer did, but don't get
me started about EEs and firmware...), but I did have to analyze it
for a proposal for a follow-on product that we never made - same
hardware, but the firmware would generate European rings and busy
signals, to test U.S. gear against non-U.S. signals.
I don't recall if the 8049 has a security fuse, but worst case, you
might be able to pull the microcontroller and get a dump of the
firmware. ISTR it only has like 2K of EPROM on it; certainly no
more than 8K.
Ethan Dicks, A-130-S Current South Pole Weather at 30-Apr-2004 21:40 Z
South Pole Station
PSC 468 Box 400 Temp -87.5 F (-66.4 C) Windchill -126.9 F (-88.3 C)
APO AP 96598 Wind 8.30 kts Grid 127 Barometer 674.4 mb (10836. ft)