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ThunderBird Avenger
TM
PCI Audio SAA7785
Accelerator
Philips Semiconductors Preliminary Specification
1999 Nov 12 15
SERIAL PORT INTERFACES
OVERVIEW
The SAA7785 chip will contain an S/PDIF Consumer Grade transmit port and an I
2
S transmit/receive pair. These serial
ports are designed to exchange digital audio data but can be used for any type of data transfer assuming the bandwidth
is adequate. Currently, these ports are connected to the DSP data bus.
The Inter-IC Sound Bus, or I
2
S Port, is a simple interface used to transfer digital data from one source to another. The
interface is based on a continuous serial clock that determines the data rate along with the word select line and the data
lines. An I
2
S port can be a master or a slave device. A master device drives the serial clock and word select lines while
a slave device receives the clocking signals. The SAA7785 I
2
S ports are independently programmable to be either a
master or a slave and for 32.0, 44.1 and 48.0KHz stereo data transfer.
Also included is a Sony/Philips Digital Interface Format, or S/PDIF, serial port. This interface is generally used to trans-
mit raw audio data but is also used to transfer AC-3 encoded data as well using DMA. The S/PDIF format is a synchro-
nous interface with the clock encoded on the data stream. The S/PDIF ports support 32.0, 44.1 and 48.0KHz stereo
data transfer up to 24 bits. The S/PDIF interface is IEC958 Consumer Grade compliant.