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By bscardin
#141704
I am having some trouble writing to the OpenLog using an MSP430 (TI Launchpad). I am able to read from the OpenLog TXD -> MSP430 RXD and am getting the "12<" into the chip. But I am having problems with the MSP430 TXD -> OpenLog RXD. I have verified the protocol using an FTDI basic and a logic analyzer hooked up to both the OpenLog and to the MSP430.

Specifically, whenever I have the OpenLog RXD pin connected to the MSP430 the OpenLog LED's flash back and forth very rapidly and then after about a second the blue LED begins to flash steadily. If I connect the FTDI to the TXD I do not see any errors across the serial interface (like I do when there is no card for example). I connected a logic analyzer and verified that this flashing is happening before the MSP430 even sends any data. In fact I can reproduce this if I just connect the RXD pin to GND (which should be OK right?) which should be the same as an idle serial line right?

Does anyone know what rapid LED flashing followed by slow blue LED flashing means?
By bscardin
#141725
Well, I think I've mostly answered my own question. When the MSP430 is configured to do UART (bit banged in this case) the TX pin is configured as an output. The problem is that the MSP430 output pin is low impedance and therefore is effectively a ground when it is set to low (i.e. idle UART). So, when OpenLog is powered up and the MSP430 UART TX is idle then the OpenLog RXD pin is connected to GND. Down in the troubleshooting section of the OpenLog datasheet it describes that connecting RXD to GND on power up will essentially do a factory reset of the OpenLog.

So, my current workaround is to set the MSP430 TX pin direction to input while powering on the OpenLog. Once it has powered on I put it back to output in order to write the data and things seem to be working better now.
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