Changing PLL settings for 24Mhz XTAL

STM32duino bootloader aka Maple bootloader
victor_pv
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Re: Changing the XTAL frequency

Post by victor_pv » Tue Sep 05, 2017 2:13 am

That looks like some sort of light controller, but can't figure out what the THn pins would be other than thermistors.

C_D
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Re: Changing the XTAL frequency

Post by C_D » Tue Sep 05, 2017 2:16 am

victor_pv wrote:
Tue Sep 05, 2017 2:13 am
That looks like some sort of light controller, but can't figure out what the THn pins would be other than thermistors.
Correct on both counts, it has both lights and thermistors, though the lighting isn't really 'controlled' as such. It could just a easily be on a separate board but its all on one for testing.

victor_pv
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Re: Changing the XTAL frequency

Post by victor_pv » Tue Sep 05, 2017 5:01 am

OK that makes more sense, I was trying to figure out what had the led drivers to do with thermistors, and a bunch of what looks like USB connectors...

Check the reference manual to see if the 24Mhz XTAL is supported if you use the /2 setting to the input of the PLL, perhaps 24 is over the theoretical limit of the PLL only, so dividing it by 2 before it enters then multiplying by 6 may be within the specs.

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RogerClark
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Re: Changing the XTAL frequency

Post by RogerClark » Tue Sep 05, 2017 5:36 am

Victor

The data sheet says

"4-to-16 MHz crystal oscillator "

I presume this to mean that the oscillator circuit e.g. the resonant components inside the MCU (mainly capacitors) are tuned to work in that range.

It probably means that if the MCU gets too cold or too hot, it won't be able to start the osc

C_D
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Re: Changing the XTAL frequency

Post by C_D » Tue Sep 05, 2017 8:01 pm

Ah yeah so I'm not actually overclocking the core am I, the internals of the MCU are all running as intended, its just the oscillator circuit thats running outside of spec. I will keep that in mind while testing these boards and make sure that future revisions have an 8MHz crystal.

Victor

The board has a 7 port USB hub with one of those ports hard wired to the STM32. When connected to the host it allows communication with the STM32 via CDC and also 6 more downstream ports for connecting additional boards and or other peripherals (USB modem, bluetooth dongle etc). The host is a single board computer running Linux which provides network connectivity and runs a touch screen HMI.

Roger is correct it is for controlling industrial equipment, this particular version has 6 thermistor and 8 digital inputs (digital in, pulsewidth or frequency measurement), 4 digital outputs (digital or pwm) and 4 relays. It also has an AC power monitoring IC for tracking line voltage and current draw of the devices connected to those relays. I guess in essence its a glorified PLC with a more targeted feature set that's not programmed in ladder :lol:

This particular combination of inputs and outputs probably wouldn't exist on a final product, if it actually gets out of the prototype stage there would be a new PCB with just the required features for the application.

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