strange behaviour

RFM12 Wireless module discussion.

strange behaviour

Postby budziq » Tue Aug 05, 2008 12:12 pm

Hi! I'm writing this post couse I cannot figure out whats going on by myself. I successfully activated one of my module. It responses to commands I'm sending by SPI. Everything is ok with it. But I've got problems with other two. I've connected them the same way, and there's something very weird with'em. They only response to first 0x0000 (read status) command showing that they've completed power on reset. Then anything I send through SPI is ignored! Also there is constant "0" on nRES pin, unlike the first one. I'm very upset and cannot figure whats going on. Some details: I'm using Atmega 644 to connect to modules, I'm working on wired board (haven't done PCB board yet). Can It be some problem with power supply, to be honest I don't believe it couse power lines look OK on scope. Also signals on SPI that I'm sending look OK. I would be very thankful for any idea what I'm doing wrong.
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Re: strange behaviour

Postby seaton » Tue Aug 05, 2008 3:14 pm

budziq wrote:Hi! I'm writing this post couse I cannot figure out whats going on by myself. I successfully activated one of my module. It responses to commands I'm sending by SPI. Everything is ok with it. But I've got problems with other two. I've connected them the same way, and there's something very weird with'em. They only response to first 0x0000 (read status) command showing that they've completed power on reset. Then anything I send through SPI is ignored! Also there is constant "0" on nRES pin, unlike the first one. I'm very upset and cannot figure whats going on. Some details: I'm using Atmega 644 to connect to modules, I'm working on wired board (haven't done PCB board yet). Can It be some problem with power supply, to be honest I don't believe it couse power lines look OK on scope. Also signals on SPI that I'm sending look OK. I would be very thankful for any idea what I'm doing wrong.


nRES should be tied high so If there is "0" on nRES you need to pull this pin high.

Are you using the the DIP version? how are you connecting to your board? make sure length of wires if soldering onto DIP module are short in length.

A couple of things to try
1) Make sure that at the start of each SPI command you lower the nSEL pin, then when you have sent the command raise the nSEL, this needs to be done for each SPI command.
2) check voltage is within specs (~3.3v)
3) put a decoupling capacitor across the VDD and gnd on the RFM as close as possible to the RFM12 module.
4) If MCU is at 5V and RFM at 3V is there any level conversion occurring?

Stephen...
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Re: strange behaviour

Postby budziq » Tue Aug 12, 2008 9:56 am

Thanks for help. I have smd module connected with wires. Apparently it was pretty dumb idea. It finally started to work after only fourth time resoldering it. I just didn't expected it to be so sensitive.
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