C5502: McBSP with external clock

Posted by PetzMein

on Nov 05 2008 02:14 AM

Dear all

We would like to clock the receiver-section of the McBSP on a 5502 device with external generated 4.8MHz.

This clock shall be used as input to the sample-rate generator (SRG), which divides down the clock to provide a lower clock to the transmitter.

The datasheet and SPRU592E (McBSP Reference Guide) are not very detailed concerning this topic. It should be possible with SRG input clock
selection from CLKR pin, CLKXM set to 1 (internal CLKX driven by SRG) and CLKRM set to 0 (CLKR pin is an input).

Is it possible to use the McBSP in such a configuration?

Thanks in advance

Peter

Posted by BrandonAzbell

on Nov 05 2008 08:26 AM

Guru55185 points

PeterM

We would like to clock the receiver-section of the McBSP on a 5502 device with external generated 4.8MHz.
This clock shall be used as input to the sample-rate generator (SRG), which divides down the clock to provide a lower clock to the transmitter.

The datasheet and SPRU592E (McBSP Reference Guide) are not very detailed concerning this topic. It should be possible with SRG input clock
selection from CLKR pin, CLKXM set to 1 (internal CLKX driven by SRG) and CLKRM set to 0 (CLKR pin is an input).

Is it possible to use the McBSP in such a configuration?

Yes, it is possible based on your description. The control bits you are referencing are correct to configure the direction of the pins for CLKX and CLKR, but do not configure the Sample Rate Generator.
I draw your attention to Section 3.1 of SPRU592E (McBSP Reference Guide), which provides a good illustration of the circuit for the SRG and indicate which control register bits configure the SRG.
You will need to configure CLKSM=0 and SCLKME=1 to propagate the CLKR input into the Sample Rate Generator.

Brandon