jrh@bunker.UUCP (Jeff Hagen) (08/20/84)
xxxx Here is a little hardware problem I came across: I have and old TI thermal printer (PC100A) that works with their 58/59 calculators. I thought it might be kind of neat to interface it to my computer. I have the description of the calculator/printer interface (from the TI technical manual). problem : The five unidirectional logic lines in the interface use a 0 volt to -10 volt logic. question: Is this TI logic some sort of standard? and more importantly, Is there an easy way to interface it to TTL ? Someone suggested a high speed op amp, but isn't this overkill? (the clock frequency is about 227khz ). Thanks for listening Jeff Hagen ittvax!bunker!jrh
mlsmith@NADC.ARPA (08/21/84)
Using differential receivers working of +/- 15 volts, you can get a TTL signal out with one inversion. Some chips even have +5 volt too. good luck, mlsmith@nadc.ARPA
bmw@aesat.UUCP (Bruce Walker) (08/23/84)
<> > I have an old TI thermal printer (PC100A) that works with their > 58/59 calculators. I thought it might be kind of neat to interface > it to my computer. > > problem : The five unidirectional logic lines in the interface > use a 0 volt to -10 volt logic. > > question: Is this TI logic some sort of standard? > Is there an easy way to interface it to TTL ? > > Someone suggested a high speed op amp, but isn't this overkill? > (the clock frequency is about 227khz ). > > Jeff Hagen > ittvax!bunker!jrh This logic is a P-channel MOS standard from old calculator days. The trouble with using your usual opamp in this application is the low slew rate. Using a high-speed opamp to correct this would be overkill. Here's a fairly simple (and cheap!!) circuit which could work for your thermal printer interface: TTL input ---> | | +12 V +-+-+ ^ | | | ========= 14 | RS232 | 1/4 |--------+ line driver | of a | (Gnd: pin 7) | 1488 |--------+ \_____/ 1 | O | | V | -12 V | | 1K 5% 1/4W +-----/\/\/\/----+--------> Output: 0 to -10 V | | 1N914 or ----- \ 1N4148 \ / / general purpose \ / 10K 5% \ silicon ===== / switching diode | \ | | | V | -12 V | === (common system ground) /// One channel is shown. There are 4 drivers in one 1488 package, so you'll need two packages. Any old 1488 will do: TI (75188), Fairchild, Motorola etc. The buffer IC was chosen because of its popularity, there are interface IC's specifically for this kind of job but they are more expensive and/or scarce. The circuit was taken from the "Applications" section of the MC1488 data sheet in the Motorola 1983 "Linear & Interface IC's" data book. Bruce Walker {allegra,ihnp4,linus,decvax}!utzoo!aesat!bmw