# Unable to read tmc uart 'selector\_stepper' register IFCNT

**URL:** <https://klipper.discourse.group/t/unable-to-read-tmc-uart-selector-stepper-register-ifcnt/9704>\
**Category:** General Discussion\
**Created:** [July 28, 2023, 6:15pm UTC](https://klipper.discourse.group/t/unable-to-read-tmc-uart-selector-stepper-register-ifcnt/9704 "2023-07-28T18:15:57Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![imforpeace](https://avatars.discourse-cdn.com/v4/letter/i/9de0a6/32.png) [@imforpeace](https://klipper.discourse.group/u/imforpeace)\
**Post date:** [July 28, 2023, 6:15pm UTC](https://klipper.discourse.group/t/unable-to-read-tmc-uart-selector-stepper-register-ifcnt/9704/1 "2023-07-28T18:15:57Z")

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[klippy.log](https://klipper.discourse.group/uploads/short-url/3Wj02hBBOfSnvCVK8WL122mMx1G.log) (97.1 KB)  
Voron 2.4, RPI4  
Octopus 1.1 24V USB serial  
Mellow Fly ERCF board USB serial

Mellow Fly ERCF throws an “Unable to read tmc uart ‘selector\_stepper’ register IFCNT” error

### Describe your issue:

After about 100 hours of usage on my initial Mellow FLY ERCF board, I saw my klipper shutdown. My Fly ERCF at that point seemed to have dropped one of the heatsinks from the stepper drivers, potentially causing damage.

I have thoroughly looked at board/driver SMDs and found no issue. I have also tried jumping uart pin to another spare pin on the board to no avail.

Now here’s the funky part: I have just replaced both the board and the drivers for a brand new counterpart, flashed it for Serial connection, and the error still persists!

Here’s the tmc dump:

```auto
Unable to read tmc uart 'selector_stepper' register GCONF
========== Queried registers ==========
SGTHRS: 00000000
TPOWERDOWN: 00000014 tpowerdown=20
TPWMTHRS: 000fffff tpwmthrs=1048575
IHOLD_IRUN: 00080c04 ihold=4 irun=12 iholddelay=8
SLAVECONF: 00000200 senddelay=2
========== Write-only registers ==========
DUMP_TMC STEPPER=selector_stepper

```

Any ideas/help is appreciated.

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<div class="post-metadata">

**Author:** ![LifeOfBrian](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/lifeofbrian/32/2380_2.png) [@LifeOfBrian](https://klipper.discourse.group/u/LifeOfBrian)\
**Post date:** [July 28, 2023, 6:38pm UTC](https://klipper.discourse.group/t/unable-to-read-tmc-uart-selector-stepper-register-ifcnt/9704/2 "2023-07-28T18:38:24Z")

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To rule out a double fault: is it working fine with the other installed TMC drivers and what happens with a known good driver on the “failing” port configured as [selector\_stepper]?

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<div class="post-metadata">

**Author:** ![imforpeace](https://avatars.discourse-cdn.com/v4/letter/i/9de0a6/32.png) [@imforpeace](https://klipper.discourse.group/u/imforpeace)\
**Post date:** [July 28, 2023, 6:41pm UTC](https://klipper.discourse.group/t/unable-to-read-tmc-uart-selector-stepper-register-ifcnt/9704/3 "2023-07-28T18:41:21Z")

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The solution was to look right under the nose and figure out that I somehow left a uart\_address: 1 in the selector tmc configuration.