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Configuration for daisy chained Mini Maestros


Following on from my first thread here, I’m currently writing code in C++ to drive daisy chained sets of 24 channel Mini Maestros. It works in some cases, but I’m having some strange intermittent problems where chained devices get red error LEDs at startup and/or don’t respond. I’m still trying to understand what it’s really doing, so apologies for the mass of questions below!

Maybe there’s something wrong with my setup… Using the Pololu Maestro Control Centre app, I’ve set up the masters in “USB Chained” mode, and I want to communicate at 115200 baud. What’s the right way to set up the chained devices? I have had most success setting them to “UART, fixed baud rate” mode, but if I type 115200 into the box, I find it has turned into 115385 the next time I check. What’s going on there? Is it just a display bug?

Is “UART, detect baud rate” appropriate for daisy chained devices? If it should work, would it use the same communication speed as is being used to talk to the master?

I have the chained devices set to get their power from the servo supply using the blue jumper block, but the masters are set to get their power from USB. Is that a sensible arrangement? Do I have to be careful about the order in which the servo and computer power is turned on?



I am sorry you are having trouble with your Maestro setup.

The chained Maestros should use the “UART, fixed baud rate” serial mode, and they should have the same baud rate as the master devices. The “UART, detect baud rate” mode should work too, but it adds extra complexity so I would recommend using a fixed baud rate instead.

The baud rates that the Maestro can exactly generate are all of the form F/N, where F is the instruction frequency (about 12 MHz) and N is a whole number. To get a baud rate close to 115200 baud, the Maestro sets N to 104, giving a baud rate of approximately 12000000/104 = 115385. This is close enough to 115200 that it works fine.

I do not think the order that you turn on the power supplies matters much. If you are not using the TX lines of the slaves, then it would make sense to turn on the servo power supply first before powering the master devices. That way, the master Maestros will not end up partially powering the slave Maestros through their RX lines. That would be undesirable, but it does not usually cause any major problems.