LPC536: Can not enter background mode after changing a register

[jsoccerd]

I'm programming with a custom board that has the LPC536JBD64 processor. The first board I changed the MAINCLKSELA register in the SYSCON peripheral to use the FRO1mhz clock. Then I got a programming error stating that it "Can not enter background mode" with a pemicro multilink. With the pemicro Cyclone programmer I get the error 0007. I then tested a second board with different programs and the programming for that board worked fine. I then tried to recreate the issue by changing the value in the MAINCLKSELA register again and now the same problem has occurred with that board. I'm assuming because I didn't enable bits for that FRO1mhz clock that the board doesn't work. But why would that cause an issue with programming the board over SWD? And is there anyway to unbrick these boards?

[jsoccerd · Accepted solution]

Found a solution on how to unbrick the board. You can use the flashmagic tool and select a processor with a similar enough flash and RAM memory to flash a new program on the board. There is no individual support for the LPC5536.I used the LPC55S66 processor over UART setting. To set the board in ISP mode go to page 909 on the reference manual. To find the UART pins go to page 910 on the reference manual(both in Boot Rom chapter). I am still curious as to why changing the register bricks the SWD programming.