PaulZC
April 9, 2026, 6:10am
21
Hi Colin (@coolin ),
I see solder residue on the SPI jumper:
It looks like you selected SPI by closing the jumper, but then changed your mind and opened it again?
u-blox modules can be a bit ‘tricky’ when going into and out of SPI mode. The posts linked below may be useful. Read the whole thing - especially this post .
To get your modules communicating again, you may need to reset the module via UART with a UART-USB cable and u-center - and probably put it into SAFEBOOT mode first.
I hope this helps,
I would like to use SPI to communicate with my GPS-RTK2 (ZED-F9P). According to the hookup guide, this can be accomplished by closing the DSEL jumper on the back of the board, and doing so should disable the UART1 and I2C ports. This isn’t working.
I’ve soldered over the gap in the DSEL jumper, connected SCK, MISO, MOSI, and a CS pin to my micro, and I get nothing. This is the same SPI bus which hosts another working SPI device, so I know the bus works.
I modify the SparkFun_u-blox_GNSS_Arduino_Library code to enable debug logging via Serial and I see this, repeating:
Sending: CLS:CFG ID:RATE Len: 0x0 Payload:
sendSpiCommand: B5 62 6 8 0 0 E 30
sendCommand: Waiting for ACK response
waitForACKResponse: TIMEOUT after 1100 msec.
I hook up a logic analyzer and quickly realize that what I believe to be SPI MISO is still UART1 TX at 38,400 baud, reading out perfect NMEA sentences.
Does anyone know why closing the DSEL jumper did not switch the board to enable SPI and disable UART1? Do I…
Dear Sparkfun
since years we are successfully working with your products, mostly Thing Plus MCU boards and also GPS with ZED-F9R.
with that setup in the end we are mostly able to work how we need (SPI interface between the two and also a third Dual-port shield parallel on SPI).
In last months we wanted to start use also the other variant of ZED-F9P.
so ordered two board (GPS-16481) and after a brief setup already stumble in SPI problems:
I soldered the DSEL jumper and connected all the SPI lines, also update all the ZED-F9P firmware via U-Center.
anyway in the end only one of the two works via SPI, the second doesn’t (maybe few time did..) but via I2C works fine.
Also checking in the forum find out that this was an issue (not sure if from Ublox or from your boards).
in the end thought that maybe just one of the two board was defective and so order two more (this time without SMA, GPS-15136).
unfortunately yet both of the two are showing the same SPI limitations, almost no one…
