You need to operate the McBSP in clock-stop (SPI) mode. Set it up as SPI|
slave device it will use external frame/clock/data inputs from your serial
device. I remember seeing waveforms in the book showing how to set up the
start bit timing relative to clock, etc.
If you're not in clock-stop mode, the clock must be running continuously (or
at least several cyles previous to the data receive) as you've discovered.
In clock-stop mode the clock is only running during data
-George > From: Jagdish prasad <>
> Subject: Observation
> Hi all,
> I was working on serial interface(MCBSP) of DSP C5410. And was trying to
> transmit/receive data from another device serial device. MCBSP serial port
> assumes that clocks should always be present, not only when data is
> We came to this conclusion by looking figures in the documents. Becausae
> is not mentioned any where in the document. We refered Enhance Peripherals
> document (spru320.pdf).
> My serial device which is communicating to DSP give the clock and data at
> the same time. When the data is not present it stop the clock. I
> DSP serial interface(MCBSP) to take clock&frame sync as input from
> Just after initializtion of receiver and transmitter of MCBSP, I gave data
> as wel as clock . It looses first 2 bit, so second word's 2 bit msb
> bit lsb of first word. same thing repeated afterwords.