working on an LPC824 project I re-used the IAP routines of an older LPC1768 project which worked fine there. These IAP routines use a common buffer for both command input and result output. The user manual explicitely allows this to be done.
Unfortunately this doesnt work with the LPC824 (at least Rev. 1A). You will always get an INVALID_COMMAND code as result. It looks like the IAP routine writes to ComRes too soon an kills its own command.
So the user manual (UM10800) is wrong here and you HAVE TO use two different buffers.