LPC122x UART0 Modem Interrupt

[martinkoehler]

Hi,

my LPC122x gives me an interrupt on UART0 with IIR - INTID (bit 3:1) containing the value 0x0. The UM10441 states this is a modem interrupt. But the UM gives no further info on this interrupt and the next page even states the value "0000" is reserved. So in the end I am confused what caused the interrupt and how to stop it (not knowing why is never good and it's also a minor performance issue).

MCR and MSR register are 0x00 so Modem is not used at all...

Martin

P.S. just found a "Modem status interrupt generation" Table in the doc naming an "enable modem status interrupt" flag "ER[3]" but no link or info as there seems to be no ER register around. Maybe IER but that is used as IER[7] just in the next coulum so I doubt it. IER[3] is marked as reserved so it might at least match as it is not anything else...but even if: the value if IER is 0x05 for me so not set -> should be no problem

P.P.S.

refering to

https://www.nxp.com/docs/en/user-guide/UM10441.pdf 

[martinkoehler]

As I already said: IER is 0x05 (or 0x07 when sending is active) so the IER[3] is not set. Even though IIR gives me this "reserved" value. Even though the interrupt itself seems to be triggered by the Send Buffer Empty Interrupt. The issue is about the wrong IIR value...

[kerryzhou]

Hi Martin,

   Please debug your code in the IDE, put a breakpoint in the UART interrupt, then after the interrupt happens, please give me a screen shoot about it, the picture should contains the register, IIR, and IER.

Have a great day,
Kerry

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[kerryzhou]

Hi Martin,

   Thanks to point this question.

   From my own opinion, I think this should be the LPC122X user manual bug. I think:

   IER[3] is the enable modem status interrupt bit.

   IER[7] is CTS interrupt enable bit.

Please clear IER[3] and IER[7] bit, then check whether your interrupt still can triggered by the modem interrupt?

After you test it, please let me know the result. Then I will report this doc bug to our according department.

Have a great day,
Kerry

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------