SWCLK pull-down/pull-up

[majbthrd]

Just a friendly FYI for any future PCB revisions:

At the moment, the EzSBC board has a 100k pull-down "R2-2" that is in conflict with the internal pull-up on SWCLK. One can see that the signal is mid-scale by probing the signal. CMOS inputs generally don't like mid-scale signals, and this resultant resistor divider circuit adds a bit more current consumption too.

A pull-down is not desirable, as the SAMD21 has a feature called "CPU reset extension" (see Section 13.6.2) where SWCLK is sampled when the external reset is triggered. That is why section 39.1.1 of the SAMD21 datasheet states "a pull-up resistor on the SWCLK pin is critical for reliable operations".

So, perhaps it is worth considering replacing the pull-down with a pull-up?

[EzSBC]

Thanks for the info. The board needs a revision to isolate the battery sense resistors in sleep mode.  I will revise it soon and fix this issue. I have been looking for the cause of high sleep current on the board. Nothing really excessive but higher than the datasheet numbers.  I have duplicated the core in a few places on customer specific boards and it is reliable. Daniel Jul 18, 2021 12:41:30 PM majbthrd ***@***.***>:

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Just a friendly FYI for any future PCB revisions: At the moment, the EzSBC board has a 100k pull-down "R2-2" that is in conflict with the internal pull-up on SWCLK. One can see that the signal is mid-scale by probing the signal. CMOS inputs generally don't like mid-scale signals, and this resultant resistor divider circuit adds a bit more current consumption too. A pull-down is not desirable, as the SAMD21 has a feature called "CPU reset extension" (see Section 13.6.2) where SWCLK is sampled when the external reset is triggered. That is why section 39.1.1 of the SAMD21 datasheet states "a pull-up resistor on the SWCLK pin is critical for reliable operations". So, perhaps it is worth considering replacing the pull-down with a pull-up? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub[#1], or unsubscribe[https://github.com/notifications/unsubscribe-auth/ARSDOQ2CIVAXLMUZL2T4633TYMU5XANCNFSM5ASN6I6Q]. [data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAFQAAABUCAYAAAAcaxDBAAAAAXNSR0IArs4c6QAAAARzQklUCAgICHwIZIgAAAAySURBVHic7cEBDQAAAMKg909tDjegAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAeDVulAABbzDScQAAAABJRU5ErkJggg==###24x24:true###][Tracking image][https://github.com/notifications/beacon/ARSDOQ7TOANPX5L3TSGFIGTTYMU5XA5CNFSM5ASN6I62YY3PNVWWK3TUL52HS4DFUVEXG43VMWVGG33NNVSW45C7NFSM4ODTVL4Q.gif]