TOIM5232 (TOIM4232, TIR1000, HSDL7001, MCP2120) SIR encoder/decoder trouble - Page 1
Forum section: electronics / projects

author: helge
author_rank: Regular Contributor
timestamp: September 19, 2014, 10:04:44 pm
content: Here is my failed attempt to use TOIM5232 for optical uart over a few meters without invoking bluetooth. The TOIM5232 refuses to do the one single thing it is supposed to (trim and stretch uart pulses for low power IR transmission) when used in my circuit. Perhaps someone can help, please.parts and setup in question:- TOIM5232 (older Vishay Telefunken datasheet for TOIM3232http://www.promelec.ru/pdf/toim3232.pdfmanufactured in a 0.8µm process, TOIM5232http://www.vishay.com/docs/81749/toim5232.pdfjust branded "Vishay", 0.35µm process, thus potentially a re-design)- SIR IrDA transceiver (low serial optical interface)- the µC attached to the codec chip runs at 5V, "all I/Os" are supposed to be 5V-tolerant- 7.3728MHz clock is supplied by an external crystal (the clockspeed itself is valid, whether this only applies to external crystals or to external clock sources as well is not specified)- exposed pad is not specified, measurement shows no resistive or diode paths to any pinThe darn thing doesn't do anything at all. Circuit description / observations:- all levels are stationary (S1, S2 outputs are high as well as RXD, TD_IR, RD_IR)- Reset and BR/D (baudrate config / !Data mode) are low for normal operation- device can be reset manually after power-up, no change- uart data coming from TXD don't sow up on TD_IR- SIR pulses properly received by a TFDU4101 SIR transceiver show on RD_IR but no data shows on RXD- I've gone through the trouble of unsoldering two chips and attached some wires afterwards (GND, VCC, XTAL1, XTAL2), connecting an external crystal does not produce a signal from the internal oscillator circuitry- supply rail sequencing: 3.3V rail rises first, 5V rail for µC follows 1-2ms later with the same rate of rise- current draw is below 1mA @ 3.30VWell, obviously something is going wrong. Maybe the external clock source peak voltage is too high which fries the clock circuitry, maybe you're supposed to inject the clock into the other pin (not supported by TOIM3232 and TOIM4232, 5232 datasheets). I'm out of luck here. Can anyone guess what the problem is here? I have some TIR1000 vom Ti here but they don't have an internal clock divider and force me to supply 16xCLK which would force me to reduce the µC speed from 7.3828MHz down to 1.843 MHz (the only timer/counter unit in the QFN28 package µC is already used to drive a charge pump)Any help would be much appreciated.

author: helge
author_rank: Regular Contributor
timestamp: September 20, 2014, 04:30:23 pm
content: I spent my last TOIM5232 trying to narrow down the error. I assume that "all pins are 5 V tolerant" does not apply to the clock pin. The external clock amplitude is 3.3V, anyway and the fact that the internal oscillator won't run with external crystals (after having had the 3.3V clock hooked up) suggests that it is blown. Mildly frustratingThe next design iteration now features a Texas Instruments TIR1000PW, "16xCLK" (1.8432 MHz) will be provided by another timer unit in the microcontroller.Conclusion : TOIM5232 may require a series resistor in the external clock line to survive!edit: now using TIR1000, works a treat.