Message Edited by rocco on 2006-07-13 09:57 PM
RS-485 is an electrical only spec.
You don't programme it, you use hardware to convert the TTL/CMOS signals that come out of your MPU into RS-485 compliant signals.
You will probably be using some kind of serial _protocol_ over the serial link, this is what you will be _programming_
In addition to what rhinoceroshead has said, here are some additional considerations -
Hello again Mingyee,
Some further comments about the digital sampling requirements for the audio signal. To achieve the full dynamic range that mu-law compression is capable of, your linear sampling resolution would need to be 14-bits minimum (13-bits plus sign bit). For A-law compression the minimum sampling resolution is 13-bits (12-bits plus sign bit). A-law has a lesser dynamic range than mu-law, but this difference is not particularly noticeable in practice.
A further reduction in the sampling resolution to 12-bits, or 10-bits, will noticeably degrade the dynamic range that you can achieve. For the case of 10-bit resolution in conjunction with mu-law, the dynamic range reduction would be 12dB. The practical effect of this is that low level audio signals will "disappear".
I am not familiar with the DSP devices, but if they have integral A/D converters with higher resolution (e.g. 16 bits) this might further dictate your choice.
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