Skip to main content
Andrew Neil
Andrew Neil
Super User
December 1, 2017
Question

STM32L0x3 and STM32L0x2 - ADC_SMPR confusion

  • December 1, 2017
  • 1 reply
  • 1031 views
Posted on December 01, 2017 at 17:55

References:

STM32L0x3 - RM0367, Rev 5

STM32L0x2 - RM0376, Rev 4

In both cases, the description of ADC sampling time register (ADC_SMPR) says,

Bits 2:0 SMP[2:0]: Sampling time selection

These bits are written by software to select the sampling time that applies to all channels.

000: 1.5 ADC clock cycles

001: 3.5 ADC clock cycles

010: 7.5 ADC clock cycles

011: 12.5 ADC clock cycles

100: 19.5 ADC clock cycles

101: 39.5 ADC clock cycles

110: 79.5 ADC clock cycles

111: 160.5 ADC clock cycles

But, in both cases, the code examples say,

(4) Select a sampling mode of

111 i.e. 239.5 ADC

clk

So which is it - 160.5 samples, or

239.5

samples??

https://community.st.com/message/75668

, from March 2015, quotes 

RM0367, v2 :

RM0367, v2, section 14.13.6 lists the following possible sample time:

1.5, 7.5, 13.5, 28.5, 41.5, 55.5, 71.5, 239.5.

https://community.st.com/message/75668

 

I don't see anything mentioned in the Revision Record...

#stm32l0x2 #adc-sample-cycles #adc_smpr #adc #adc-sampling-time #stm32l0x3
This topic has been closed for replies.

1 reply

Andrew Neil
Andrew NeilAuthor
Super User
December 1, 2017
Posted on December 01, 2017 at 18:24

I found an old Rev 2 copy of RM0367 - and it does, indeed, say:

Bits 2:0 SMP[2:0]: Sampling time selection

These bits are written by software to select the sampling time that applies to all channels.

000: 1.5 ADC clock cycles

001: 7.5 ADC clock cycles

010: 13.5 ADC clock cycles

011: 28.5 ADC clock cycles

100: 41.5 ADC clock cycles

101: 55.5 ADC clock cycles

110: 71.5 ADC clock cycles

111: 239.5 ADC clock cycles 

http://www.mouser.com/ds/2/389/DM00095744-337294.pdf

  

So was that a chip revision?

Or an error in the earlier document, that's been partially fixed?

Or an error that's crept into the new document?

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
waclawek.jan
waclawek.jan
Super User
December 4, 2017
Posted on December 04, 2017 at 23:37

Andy,

The first is unlikely; both of the second two have been seen many times.

Did you try, what is the sampling time in reality? (Yes I know I know it needs to come from ST, but that may take quite long).

Jan

Andrew Neil
Andrew NeilAuthor
Super User
December 5, 2017
Posted on December 05, 2017 at 16:40

No, I haven't tried it. The timing is not critical for me at the moment, so I have just left it at max.

Given nearly 1000 pages of reference manual, one doesn't expect to have to reverse-engineer the product oneself ...

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
Terms & ConditionsAccessibility statement