/* Thu 01-25-1996 4-buck serial link V 1.01 WARNING ======= The COM port of a PC is usually well protected against shorts and such. But I don't know about the protection in the calculator, so BE CAREFUL. SCHEMATIC (if this is garbled, see the end of the document for another view) ========= Sign 9-pin 25-pin TI8x connector DSR 6 6 o컴컴컴컴컴� � 旼컴커 � DTR 4 20 o컴�3.3k쳐컨컴컴컴컴컴컫컴컴훟 white, middle 읕컴켸 � � � � �\ � LED �\ � � � GND 5 � 7 o컴� >쳐컴커 旼� >쳐� � max +5V � �/ � � � �/ � 4.7V zener � � +2V � � � � 旼컴커 � � V TXD 3 V 2 o컴�330R쳐컨컴쩡좔컴컴컴컴컴훟 screen, base (TI ground) 읕컴켸 � ^ � �\ � 4.7V zener � CTS 8 5 o컴컴컴컴컴� 읕캑 >쳐� � max +5V � �/ � � � 旼컴커 � � � RTS 7 4 o컴�3.3k쳐컨컴컴컴컴컴좔컴컴훟 red, tip 읕컴켸 PARTS LIST ========== 2 3.3k resistors 1 LED (or something with about 2V drop) 2 4.7V zener diodes (Radio Shack 5.1volt Zener Diodes work fine) 1 330R The resistor values are not critical, +- 20% is close enough. The zener diodes are more critical, because they control the voltage reaching from the PC to your calculator. The LED gives a nice shine, but also shifts voltages on PC inputs (DSR and CTS) towards negative. Some PCs can work with no LED, some require an LED which gives about 1.5 to 2V drop. The RS232 standard requires inputs to work with +-3V signals, so this circuit does not comply with the standard (but seems to work). I assembled the link by obtaining a connector for the PC's COM-port and soldering the components directly to that. Then I cut a calculator-to-calculator cable in half and soldered one piece to the connector. TESTING ======= Connect the cable to your PC, BUT NOT YET TO THE TI8x, with no link program running, (DTR and RTS at less than -5V) The voltages from 'red' or 'white' to the 'screen' should be -0.7V. Start a link program on your PC, this should turn the link into idle state (DTR and RTS to more than +5V) and the voltages from 'red' or 'white' to the 'screen' should now be 4.7V. If you have made the measurements with correct results, then you can connect the link cable to your calculator. If your calculator 'freezes' (ie. becomes slow) then there is something pulling the signals (red and white) to ground, OR you have not pushed the connector far enough into your calculator, OR you have not started a link program, which places the link into idle state. The system has been tested on a 20MHz 386 and a 75MHz 486 PC, and with TI-85 and TI-82 calculators. All four combinations work well. WARRANTY ======== I GIVE NO WARRANTY NOR TAKE NO LIABILITY FOR ANY OF THE IDEAS EXPRESSED HERE. So take your time to make sure everything is COOL (literally:-) FAQ answers =========== -I do not know where you can obtain the components -This ought to be compatible with some other link software, but I don't know exactly which one(s) -The software (TI.EXE) works with TI-85 and TI-82 program files, group files and memory backups (at least). (TI-82 backups require version 1.01 or later) -For Mac and Amiga and ... this works, IF you can get the software to drive it (not from ME) Timo timo.stenberg@ntc.nokia.com SCHEMATIC in 7-bit ASCII ========= Sign 9-pin 25-pin TI8x connector DSR 6 6 o----------- | ------ | DTR 4 20 o--|3.3k|--+-----------+-----o white, middle ------ | | | | |\ |LED |\ \ | | GND 5 | 7 o--| >|----- --| >|-- | max +5V | |/ | | | |/ \ | | +2V | | | | ------ | | 4.7V zener V TXD 3 V 2 o--|330R|--+--+-+------------o screen, base (TI ground) ------ | 4.7V zener ^ | | | |\ \ | CTS 8 5 o----------- ---| >|-- | max +5V | |/ \ | | ------ | | | RTS 7 4 o--|3.3k|--+----------+------o red, tip ------