DMTi
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KDS Interface Timing
The KDS physical layer interface consists of three signals; KDS Clock, KDS
Sync, and KDS Data. The KDS Clock is a clock signal whose frequency equals
208x or 256x the sample rate, for 26 or 32 bits per channel, respectively. The
KDS Sync pulse is valid for one clock cycle each sample frame, such that the
Most Significant Bit (MSB) of the first audio channel is valid in the first clock
cycle following the valid KDS Sync pulse. Audio data is represented as a 2’s
complement number where the MSB is the sign bit. Unused Least Significant
Bits (LSBs) are usually represented as zeros. One can build a KDS input inter-
face that supports both 26- and 32-bit versions by counting the clock transi-
tions between KDS Sync pulses. There are 208 clock transitions for every KDS
Sync pulse for KDS26, and 256 clock transitions for every KDS Sync pulse for
KDS32. The KDS Clock, Sync, and Data are produced as follows:
All three signals, Clock, Sync, and Data are typically produced by flip-flops
within the same device to minimize skew.
The same can be said for the differ-
ential transmitters and receivers used at each end of the cable. KDS Sync and
KDS Data change at the same time that the KDS Clock transitions from High
to Low. At the receiving end of the cable the rising edge of the KDS Clock is
used to detect KDS Sync and latch KDS Data.
This specification assumes the use of AM26LS31 differential transmitters for
driving the KDS bus and AM26LS32B differential receivers for receiving the
bus. KDS transmission lines are terminated by a single 110-ohm resistor across
the + and - inputs of the receiver.
KDS DC Specifications
KDS interface DC specifications are determined by the differential transmitter
and receiver specified, assuming a 4.75V to 5.25V interface supply voltage. The
output voltage swing is typically 3 Volts. Typical cable attenuation for 15
meters of Belden 9806 results in a swing of approximately 2 Volts at the re-
ceiver. Ground potential difference between the KDS transmitter and receiver
should not exceed 1V.
KDS
CLOCK
KDS
CLOCK
KDS
CLOCK
LSB+1
LSB - Channel 7
MSB - Channel 0
MSB -1