I need to use LMX2541, three, for a measurement system.
Two of them, have a relation of 60 MHz difference, so i would like to change the frequency simultaneously.
Can you recommend a microcontroller, to do this?
You could use just about any microcontroller, there are not many system details here of how the CPU interacts with other system elements. I might recommend one of the MSP430. You could pick a device with two SPI ports to program the devices, or you could bit-bang the outputs. Often microcontrollers with SPI support will leave control of the LE pin(s) up to the user to bit bang while automating the CLK&DATA lines.
Possible choices include:
> The MSP430F5308 has two SPI ports.
> The MSP430G2001 is very low cost and could be programmed to bit bang the outputs.
The general info you need to know for your objective is:
- In systems with multiple SPI devices, it is possible to share CLK and DATA, but have an LE for each LMX device (hence the simplicity of micros which have the user bit-bang the LE).
- Your system uses 3 LMX2541, which means at least 2 + 3 = 5 IO are required.
- Because of your requirement for two devices to change frequency simultaneously, an extra clock will be required (6 IO) so that data can be clocked into the 2nd device without impacting the data of the other LMX to change frequency. After loading data into the two LMX devices, the LE of both of these devices should be toggled high at the same time. Please see the illustration below:
If using a micro with two SPI ports, then the DATA123 pin may be broken into two pins, DATA1 and DATA23.
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