am having problems at power up & power down, the codec output is clicking. At
power up, Looking at the output of the codec, it seems to charge up to it's
bias voltage very slowly, and some time after the codec is brought out of
reset, the bias voltage 'jumps' to 1/2 vcc, which causes a click at the output.
Do you have any recommendations about how to safely drive the codec from an
ADSP-2185 DSP without causing output pops ?
Generally speaking, the problem of power-on and power-off clicks is found in
many audio systems. One solution is to use an output drive amp which is
disabled on power-on and power-off and only enabled (gradually) once the rest
of the system has finished all it's clicking and popping. A part like the
SSM2250 is designed to do this job.
A general reference for using our AC 97 CODECs with DSPs is the application
note on using the AD1819A with the ADSP-21065.
There are loads of application notes which deal with using the AD1847 sound
port CODEC with ADSP-218x DSPs, but the AD1881 is a different generation of
CODEC and I'm not sure how much of the material will be useful for you.
AD1881 was replaced by AD1881A in January 2000.