TIC500 - RPi4 - De-energize Command on UART3 Impacts Device on UART4


I am at a loss as to where to start troubleshooting this issue.

I have Raspberry Pi 4 Compute Module (inside of a Seeed reTerminal) with both UART3 and UART4 enabled, as /dev/AMAtty1 and /dev/AMAtty2, respectively. And am using Node-Red to program it all.

On UART4, I have a TIC500 with an Actuonix S20 Stepper Actuator attached. With assistance from Brandon here @ Pololu on this forum, and a number of other resources, I finally learned how to structure the commands to make this work. And it works very well.

EDIT: Also, am using Pololu Protocol to structure the Serial commands to the TIC.

On UART3, I have a Serial Bus Servo running directly off the Pi, no dedicated controller, which is also functioning well.

Where it gets odd to me, is that if I send a De-energize command to the TIC, afterward, a number of the Servo commands start throwing errors when sent, and the return data from the Servo is invalid. If I then send an Energize command to the TIC all returns to normal. This happens regardless of whether the “Ignore ERR line high” setting is set.

First, in my application, I would prefer not to have the Actuator energized at all times as it gets pretty hot. And second, I do not understand how issuing a command to a device on one UART could impact the operation of a device on another UART.

If anyone can provide any insight and/or direction as to aid in troubleshooting, I would be very appreciative. Also, if I need to provide further information, please let me know.


It is not clear to me how de-energizing the Tic would have any affect on the communication with your servo on a different serial bus. Does your serial communication with the servo work fine when the Tic is disconnected from your system? Could you post some pictures of your setup that show all of your connections?


Thanks Brandon,

I am puzzled, as well. That’s why I created this thread.

BUT, also, since I’ve expanded my code to add functionality, and to include various other command and data manipulations, I am not now able to recreate the UART3 serial command errors. Thinking back on what I’ve done since the errors, I cannot identify anything that should’ve resolved the issue. From a hardware perspective, I changed nothing since posting this thread.

If the situation recurs, per your request, I will update with more information and pictures.

Again, thank you for your quick response.

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