Can TM4C123 shares a 12MHz crystal

Hai Dinh

Hello everyone,

I'm moving from prototyping with Tiva C launchpad to making a circuit board using TM4C123. The MCU on launchpad uses a 16MHz crystal (Y2) as its main clock.

On my circuit board, however, I have a 12MHz crystal (for other component). I wonder if I can just supply this crystal clock to pin OSC1 and OSC0 to reduce BOM and space.

Should I change some setting (TI-RTOS) to tell the MCU that it is supplied with a 12MHz clock or the MCU will automatically recognize the clock frequency?

Thanks.

over 9 years ago

0 Amit Ashara over 9 years ago

TI__Guru**** 244400 points

Hello Hai,

No. Do not share the clock pins. You would end up losing more on the end product than saving on the BOM and space. Please use separate crystals or have a CDC device if only one crystal is to be used.

Yes, the TI RTOS needs to be updated for the 12MHz crystal.

Regards
Amit

0 Hai Dinh over 9 years ago in reply to Amit Ashara

Prodigy 70 points

Thank Amit, it helps a lot.

0 Amit Ashara over 9 years ago in reply to Hai Dinh

TI__Guru**** 244400 points

Hello Hai,

CDC's are generally preferred. But they provide a single ended clock.Also note on the TM4C123 a single ended clock may cause the device to consume extra current (Refer to the Errata)

Regards
Amit

0 SourceTwo over 7 years ago in reply to Amit Ashara

Expert 2355 points

Hello Amit/others,

A quick question: What is a CDC in this context? Perhaps an external oscillator? Thank you!

Regards,

Dave

0 Robert Adsett over 7 years ago in reply to SourceTwo

Guru 27665 points

Clock Distribution Circuit. They can include dividers and buffers (so each device gets its own clock signal) and may also contain skew control so the devices have a fixed phase difference. So single clock can then serve multiple devices, saving the cost of multiple oscillators.

I've never used one myself but I've run across references.

Robert

0 cb1_mobile over 7 years ago in reply to Robert Adsett

Guru 117855 points

Robert "beat me to the punch" (again.) Ratz!

Only thing to be added - while such "single" frequency generating element appears attractive - the "distribution" of the HF clock signals may cause (in reality (always) causes) some pcb signal traces to be extended! (i.e. those devices "furthest" from the CDC.)

Best to - when/if possible - route the lowest frequency signals via those "longer" trace runs... (this assumes that the CDC provides "different" output frequencies (via the dividers - Robert noted).)

0 SourceTwo over 7 years ago in reply to Robert Adsett

Expert 2355 points

Robert and cb1_mobil,

Thank you - nice to have capable and willing reference sources!

Regards,
Dave

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Can TM4C123 shares a 12MHz crystal