Monitor Mode on I2C Interface, LPC4088

alexanderplanit — Fri, 03 Feb 2017 06:42:52 GMT

Hello,

I managed to setup the I2C Interface on my LPC4088 in Monitor Mode and i can see everything that is transmitted on the bus, but i ran into a problem.

Apparently my Interface interprets all intercepted I2C-Packets (so everything between Start and Stop Condition) as Writing-Operations (aka Slave-Receiver Operation).

Meaning the State changes of the Interface (content of I2C_STAT register) look like:

0x60 -> 0x80 -> 0x80 -> ... -> 0xA0

where the states indicate the following:

0x60: Own Slave Address + Write Bit received, ACK received

0x80: Addressed with own Slave Address, Data received, ACK returned

0xA0: Stop or Repeated Start received

However they should also be State changes like (to indicate Slave-Transmitter Operations):

0xA8 -> 0xB8 -> 0xB8 -> ... -> 0xC8 -> 0xA0

where the states indicate the following:

0xA8: Own Slave Address + Read Bit has been received; ACK has been returned

0xB8: Data byte in I2DAT has been transmitted; ACK has been received

0xC8: Last data byte has been transmitted, ACK has been received

I verified the measured protocol with an Logic Analyzer and the Results indicate that the R/W-Bit was indeed transmitted correctly.

I checked the 7-bit address + R/W-bit which is transmitted in the first byte after the start condition and the address is always correct but the R/W-bit is always '0' (but at the same time '1', when measured with the logic analyser

Here is the code i used to configure the I2C interface:

LPC_I2Cx(id)->ADR0 = (I2C_SLAVE_ADDR << 1); //Set own device address
LPC_I2Cx(id)->MASK[0] = (I2C_SLAVE_MSK << 1); //Set address mask
LPC_I2Cx(id)->MMCTRL |= I2C_I2MMCTRL_MM_ENA; //Enable I2C Monitor Mode
LPC_I2Cx(id)->CONSET = I2C_CON_I2EN | I2C_CON_AA;
LPC_I2Cx(id)->CONCLR = I2C_CON_STA | I2C_CON_STO | I2C_CON_SI; //Enable I2C Interface

I also tried different I2C-Interfaces, but the result was the same.

BOTTOM LINE:

What causes this behavior?

Is it the I2C Interface itself interpreting the R/W Bit as a '0' because its always "reading" from the Bus?

If YES, is there a way to bypass this Issue?

If NO, did I configure something wrong?

(Feedback/Suggestions/Experiences are much appreciated ;-) )

BR,

Alexander

Re: Monitor Mode on I2C Interface, LPC4088

Carlos_Mendoza — Tue, 21 Feb 2017 17:31:44 GMT

Hi Alexander,

I have a few questions, is only R/W bit got wrong and all other bits (e.g. the sequent data bits) are right? Does this issue always or occasionally occur at the same test condition? How about if only not use monitor mode?

Thanks in advance!

Best Regards,
Carlos Mendoza
Technical Support Engineer

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Monitor Mode on I2C Interface, LPC4088

Re: Monitor Mode on I2C Interface, LPC4088