Using Debug Out (p19) to program 3rd Party nrf52840/nrf52810 boards with issues

Question

I wrote some user data to 3rd party nrf52840 boards flash using the command "nrfjprog --memwr 0x1001084 --val 0x33333333" , when I ran the program the data values was not 0x333333333, 
 but running the command " nrfjprog -- memrd 0x1001084" returned the correct value 0x33333333. On the nrf52840DK I have cut the fuse in sb40 to prevent the boards 52840 chip to be programmed every time I program a chip using the Debug Out connection.The is the correct way, right? I am also trying to erase(all) of the flash before writing to it, but it doesn't help either. 
 What are the correct steps to write reliable to flash memory? 
 Thanks

Einar Thorsrud · Accepted Answer

Hi, 
 Olaf said: But you have dismissed the case that nrfjprog writes to the " nrf52840 preview DK" when DebugOut have a tag-connect cable attached. 
 Well, it depends on your HW as well. You need to short the GND detect signal to ground. If that is not done in the device end of the tag-connect cable you should instead short it to GND on the DK (for instance as shown in the image below). This is the signal that determines if the debugger should connect to the onboard nRF52 or via the debug out port. 
 
 Olaf said: How can I verify that the .hex files are transferred correctly to 3rd Party board? 
 You can verify that you are debugging the custom board and not the DK by for instance reading out the DEVICEID registers and seeing that they are different. If they are not different, then you are always looking at the same device. And if you have a LED or something on your custom board you can of course use the firmware to control it so that you can see that it has been programmed.

Using Debug Out (p19) to program 3rd Party nrf52840/nrf52810 boards with issues

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