semi-OT: text lites

On Fri, Apr 30, 2004 at 01:07:51PM -0400, John Allain wrote: 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 -- 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) Ethan.Dicks(a)amanda.spole.gov http://penguincentral.com/penguincentral.html