Create SPI interface for ADSP 21065L

[Roman Arnet]

Hi
I'm designing a mixer where 4 audio channels are digitized and mixed
together in an ADSP 21065L. The human interface has got a lot of
switches and potentiometer to control level, attacktimes ect.
- Im using low cost AD converters (12Bit) with an SPI interface to
digitize the potentiometer signals.
- A LED driver chip is accessed by SPI as well
- Some preamplifiers are daisy chained by SPI too

What I want do is to decoupelate these components from the DSP by a CPLD
because of the (rather slow) mentioned peripheral components.


++++++++++
+ + ¦---PREAMP
+ ADSP +----++++++ ¦
+ +----+CPLD+------------LED
+ +----++++++ ¦
++++++++++ ¦---SWITCHES
¦
¦---12Bit AD

The DSP accesses the CPLD by it's data/adress bus. The CPLD sends the
received data to the rigth component by SPI.

Does anybody have experiance in such a solution?
Maybe there is a better way to do that (I hope so). It would be nice if
someone would know a already existing chip doing this...
Best regards
Roman

 

[Stefan Heinzmann]

Hi
I'm designing a mixer where 4 audio channels are digitized and mixed
together in an ADSP 21065L. The human interface has got a lot of
switches and potentiometer to control level, attacktimes ect.
- Im using low cost AD converters (12Bit) with an SPI interface to
digitize the potentiometer signals.
- A LED driver chip is accessed by SPI as well
- Some preamplifiers are daisy chained by SPI too

What I want do is to decoupelate these components from the DSP by a CPLD
because of the (rather slow) mentioned peripheral components.


++++++++++
+ + ¦---PREAMP
+ ADSP +----++++++ ¦
+ +----+CPLD+------------LED
+ +----++++++ ¦
++++++++++ ¦---SWITCHES
¦
¦---12Bit AD

The DSP accesses the CPLD by it's data/adress bus. The CPLD sends the
received data to the rigth component by SPI.

Does anybody have experiance in such a solution?
Maybe there is a better way to do that (I hope so). It would be nice if
someone would know a already existing chip doing this...

While you could probably do this with a CPLD, I would rather try to use
a small microcontroller for this task. There are enough microcontrollers
with a built-in A/D converter for scanning the potentiometers. You may
also be able to drive the LEDs directly, making your LED driver chip
redundant. I bet that you would end up with a lower chip count and maybe
also lower cost.

The question is how to communicate between microcontroller and DSP. I
assume that all the DSP's serial ports are busy doing audio. One
possibility would be to make the microcontroller the host processor and
use the DSP's 8-bit host processor interface. This sounds backwards, as
the DSP is the "boss" in your system, but it would nevertheless work.
Another possibility is to make the microcontroller act as an off-chip
8-bit peripheral to the DSP. It needs a suitable communication port for
this. The Microchip PIC16C74 would be an example for a suitable
microcontroller, but there are many others.