uBlox neo-M8Q: behavior of UART TXD pin (output) during reset

0 votes
I am designing an embedded application using the neo-M8Q (Host UART interface), and the host is powered with a different supply (same ground reference).  Host supply comes up after neo-M8Q supply.  I want to make sure neo-M8Q is not driving into un-powered host.  If I hold reset active until all power supplies are up, will that keep the UART TX from driving until reset is deactivated?  I didn't see information in the state of the outputs during power up and/or reset in any of your documents or online questions.  - Thanks
by BobW asked Jul 9
0 votes
I have not seen such requirements and maybe you should modify your design by adding buffers or by delaying power to NEO-M8Q.

Holding NEO-M8Q in reset may work but I would suggest controlling LDO for NEO-M8Q, assuming you followed u-blox recommendations and have a dedicated LDO for the receiver.
by grumpy answered Jul 9
Confirming what grumpy states, and offering the same concern in the other direction:  if you have signal lines connected to the NEO that drive voltage or current into the NEO while its VCC is unpowered, then you risk irreversible damage to NEO IOs.  A quick review of forum contents shows the destruction resulting from unprotected connections (external drive of any V into IOs of unpowered modules) or mismatched IO connections  (+5 V TX line from Arduino smoking the 3.6V max of a NEO RX input pin)