Why do I get “Error: Flash download failed – Cortex-M0” when downloading a project from Keil?

Question

When I try to download code to my nRF51822 from Keil, I get this error: “Error: Flash download failed – Cortex-M0” 
 What can I do about it?

Ole Morten · Accepted Answer

There could be several reasons for this, but the most common two are: 
 
 
 That the chip is in system off . When the chip is in this mode, it is not accessible to the debugger, and hence any download will fail. You can either wake it up in some way (pressing a button configured as a wake-up, reset or similar), or use nRFgo Studio's Recover functionality. If nRFgo Studio finds a programmer, but can't communicate with the chip, it will offer to try a recovery. This will erase all contents on the chip, and in that way ensure that it doesn't enter system off again. 
 
 
 That you try to flash a program on top of the softdevice . If you have programmed the softdevice into the chip (which occupies the flash from address 0x0 to 0x14000), and then try to program an application in this same space (i.e. an application not meant for use with the softdevice), you may see this error. 
 
 
 Again, there are two ways to fix this: 
 
 Erase the softdevice. 
 Choose the nRF51822_xxyy_s110 target from the dropdown next to the Download button in Keil. All the non-BLE examples in the SDK come with project settings so that they can be used both with and without the softdevice programmed. If you set this to one of the _s110 targets, the application will be moved from address 0x0 to address 0x14000, meaing it will work nicely on top of the softdevice, even though it doesn't use it. 
 
 Edit: format.

Why do I get “Error: Flash download failed – Cortex-M0” when downloading a project from Keil?

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