LPC-LINK2 VCOM port

[nzia]

Hi,

I am using LPC-LINK2 with LPCXpresso845MAX board (for now). I could have used the 845MAX's built in 11U35 for SWD and VCOM but I choose LPC-LINK2 because that will be the board I will use when I design my own board with LPC845.

So setting up LPC-LINK2 in DFU mode and disabling 11U35 (by shorting JP1) on 845MAX board, I am able to load and run the code with MCUXpresso IDE. However I have no success in getting the VCOM working. In my test application, I have redirected the printfs to UART0 on 845MAX board which is available on J2 pin 7 and 8. And I am sure that the prints are coming out on these pins as I am able to connect an external USB serial port dongle and get the prints on my Teraterm console. However when I connect LPC-LINK2  uart pins which (I believe) as per schematics are routed on J3 pin 7 and 8 (UART2_RXD, UART2_TXD), I don't see output on console.

My question:

- Am I connecting the correct pins on LPC-LINK2 for VCOM? If not can someone tell me which pins should I connect?    

- Is there any step I am missing to get the console output.

[brendonslade]

The default firmware for the standalone LPC-Link2 uses the same port pins as the on-board version, which are P2_0 and P2_1 (not the UART2 pins you are trying to use). When LPC-Link2 was initially designed there was a long term goal to support parallel trace, which was never implement as HS USB bandwidth and available SRAM was seen as too limiting; ports P2_0 and P2_1 were used as trace port connections to the target via a buffer. 

It is possible to get a unidirectional VCOM port (from a target to the host PC via LPC-Link2) by connecting to pin 16 of the SWD/JTAG/ETM connector J8 at pin 16. Due to the buffer between the LPC4370 on LPC-Link2 (originally intended for trace data), it is not possible to get data in the other direction.

[nzia]

That is a limitation on LPC-LINK2 as it is promoted as “universal” debug probe for nxp processors.

If UART2 pins are not used for any other purpose, I think it’s a good idea NXP to support VCOM on those pins in future releases.

Let me know if that is a possibility, because in that case I will keep J3 compatible header on my board otherwise I will remove it.

[brendonslade]

Hi Nadeem,

Sorry but we wont be able to provide that support on LPC-Link2, but will be sure to address in future debug probe designs. The LPC-Link2 is still a universal debug probe (VCOM is orthogonal to SWD/JTAG debug), but I agree this is an unfortunate limitation.

regards,

Brendon

[nzia]

Hi Brendon,

      Thanks for your response. I understand your point of view as VCOM being orthogonal to SWD/JTAG. However  11U35 on various NXP evalkits  supports both SWD and VCOM, hence raises the customer's expectation for LPC-LINK2 being universal debug probe. 

       Hope to see update in new probe designs soon :smileyhappy:.