An experiment in programming the AN6311NFA PLL

Posted on Feb 7, 2014

The goal was to convert this radio for operation on the 70cm amateur radio band. This was unsuccessful as the VCO will not oscillate at the right frequencies for 70cm operation (the VCO control voltage bottoms out before the VCO gets anywhere near the 70cm band). The VCO is too small and it is too hard for me to trace the multilayer board tracks (

An experiment in programming the AN6311NFA PLL
Click here to download the full size of the above Circuit.

I do not have a service manual for this radio) so I can not change the frequency determining components of the VCO. Please note that the antenna was removed from this radio and replaced with a dummy load for these experiments. However, all is not lost. This project was a valuable learning experience and with any luck, the tools that I produced in the process (essentially a crude logic analyser) will be able to be used to reverse engineer other serial PLL control protocols. I was unable to find a datasheet for the AN6311NFA, however, I was able to find data on two similar ICs made by the same manufacturer. This, combined with my oscilloscope, allowed me to identify the serial control lines on the AN6311NFA. One board with an ATtiny2313 microcontroller (clocked at 18. 432 Mhz) and an ST232 RS232<->TTL level converter was constructed. One complication encountered was that the PLL was supplied from a 3. 3V DC power supply, when spying on the serial comms to the PLL this is not a problem as 3. 3V is enough voltage to register as a logic high on the tiny2313`s input pins (when the tiny2313 is supplied with 5v). However, when driving the PLL, care must be taken to limit the voltage on the PLL input pins to 3. 3V or less, I did this by using pullups between the PLL input pins and the radio`s 3. 3V rail and by using the tiny2313`s outputs to pull the PLL input pins low when a logic 0 was required. Three different firmware programs...

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