LPC824 return to SWDIO function

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 18, 2016 by lpcware
Content originally posted in LPCWare by tsaluzzo on Tue Apr 05 14:16:32 MST 2016
We're using an NXP LPC824M201JHI33 in our design. We're using all of the I/O pins including the ones used for Serial Wire Debug (SWD). Our application code sets the SWDIO/PIO0_2/TMS pin to general purpose output, and the SWCLK/PIO0_3/TCK  pin to SPI0_SCK output; the PIO0_12/ISP Entry pin is used as a general purpose input.

Our problem: After we change the SWDIO/PIO0_2/TMS pin to a general purpose output, it doesn't seem to return to SWDIO if we enter the In System Programming (ISP) mode by resetting the part with PIO0_12/ISP Entry held low. We don't see this problem if we just set SWCLK/PIO0_3/TCK to SPI0_SCK and leave the SWDIO/PIO0_2/TMS in its default state.

Everything I found in the data sheet and user's manual says both pins should return to their SWD functions whenever the part is reset with ISP Entry held low. I didn't find any errata for either the SWD pins or the ISP mode.