[sdiy] dsPIC interfacing with multiple CODEC chips

[Steve Lenham]

From: "Seb Francis" <seb at burnit.co.uk>

> Hi,
>
> Is there someone out there who has experience with dsPICs and CODEC chips?
>
> I'm using a dsPIC30F4013 and am wondering if there's an easy way to get it 
> to read/write to 2 CODEC chips at the same time.  The application is a 4 
> channel digital delay using 2 stereo CODEC chips.
>
> From the PIC datasheet there seems no easy way to do this, so I am 
> thinking I'm going to have to use 2 PIC chips.  But maybe I'm missing 
> something?
>
> Seb (who's always got at least 2 projects on the go at once)
>

Hi Seb,

I evaluated the dsPIC devices for a commercial project I'm working on and 
encountered exactly the same problem. Because the PICs have just one 'codec' 
port, it is hard to hook up more than one stereo converter.

It IS possible to connect several devices, but they have to be configured as 
a Time Division Multiplexed system, and most of the cheap/easy to get hold 
of/popular converters don't support that way of working. Some of the newest 
multichannel parts (intended for surround sound equipment) do, though. See 
the Cirrus/Crystal website, but good luck in buying parts like that in small 
quantities.

Try as I might, I couldn't come up with a solution to this other than using 
a programmable-logic interface between the converters and the PIC, at which 
point it seemed easier to look for another DSP. This was a real shame, as 
I'm comfortable with standard PICs and one dsPIC can do DSP _and_ controller 
duties. IMHO, Microchip really missed the ball when they implemented that 
crappy converter interface - at the very least they should have fitted two 
'codec' ports. But audio doesn't seem to be their favourite/target market, 
judging by the volume of applications vs. stuff like motor control, etc.

If you solve it, do let us know! I ended up using the Alesis/Wavefront 
AL3101, which is crappy in other ways but at least has four stereo codec 
interface ports (I needed four) and is optimised for audio.

Cheers,

Steve L.