Hi there,
I'm having an issue concerning write operation from a Microchip PIC18f microcontroller to the TI TRF7960 RFID reader over SPI. The problem is that writing to the TRF7960 only works when I put a small capacity like 10...15pf on the MOSi line (probe of my scope works as well, this way I stumbled over it in the first place...). On the scope the signals (chip select, clock, MOSI) always look the same, no matter whether the extra capacity is connencted or not connected. Without the capacity the RFID reader seems to be deaf to what ever I'm throwing at him. With the extra capacity connected to MOSI everthing works fine. You could think there a flaw in my hard or softwaredesign but my signals look exactly as described in the datasheet. I discussed the issue on microcontroller.net and I got an answer from another engineer who had the same problem a couple of years ago. He told me he forwarded this to TI support. The reason for this behaviour was most likely a soldering problem (according to the TI support guys) and somehow they fixed it by playing around with the soldering profile. Anyway, does anybody know this and is there an applicable solution?
Thanks Guys
Regards, Kristian