6.5 A Closer Look at Crown Bus Wiring
The Crown Bus is a serial communication loop de- signed to transmit IQ commands and data. As imple- mented in the IQ mixer/multiplexer, it is a 20 mA current loop operating at a baud rate of 38.4 K.
The Crown Bus connection can use inexpensive
Here are some guidelines for
•When interference is a problem, use shielded
•Minimize the total capacitance of a Crown Bus loop. The total capacitance should be less than 30 nF. Allow approximately 60 pF for each IQ component in a loop. This accounts for a slight signal degradation which occurs as data signals pass through a component.
•Add an IQ Repeater for very long
•Never use the ground wire in a mic snake line. It may sometimes be convenient to run Crown Bus data signals to and from stage monitor ampli- fiers along unused wire pairs in a mic snake. Do not use the ground wire which is normally con- nected to pin 1 on an XLR connector or data noise will be added to the audio lines. Use only the signal lines which normally connect to pins 2 and 3 of the XLRs.*
Outside RF interference is seldom a problem for a Crown Bus
*Because typical mic cables have high capacitance, the maximum possible Crown Bus loop distance will be less.
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