2.0 Functional Description
Fusion 878A
2.16 High Speed Serial Interface Mode
PCI Video Decoder
2-52
Conexant
100600B
2.16 High Speed Serial Interface Mode
The same interface used for digital audio may be used for other types of digital
serial data. With default settings, the maximum data rate into the serial interface
is 16.6 MHz, due to PCI clock resampling of the ASCLK. Changing the DA_APP
bit to 1 and the DA_IOM bits to 01 allows direct ASCLK sampling and increases
the maximum speed of the interface to 40 Mbps. The DA_SBR bit must also be
set to 1 for proper transfer to serial byte packets.
The ADATA input is clocked into an 8-bit shift register. The basic timing
relationship between the ASCLK and ADATA pins is identical to the timing in
Digital Audio input mode (refer to
). The DA_SCE bit determines
whether the data is clocked in on the rising edge or the falling edge of ASCLK.
When DA_SCE is low (default) data is clocked in on the rising edge. If
falling-edge clocking is desired, DA_SCE must be changed to 1. The DA_MLB
bit determines the bit order. When DA_MLB is low (default), the "MSB first"
format is used. If DA_MLB is high, the "LSB first" format is used.
There are two ways of getting the registered data into the audio path for
packetization. If the DA_DPM bit is low, the ALRCK signal must transition every
eighth bit to signal the input byte boundaries. (Both rising and falling edges of
ALRCK are used to clock bytes.) Alternatively, if DA_DPM is high, a 4-bit
counter is provided to eliminate the need for a continuos ALRCK. In this case, it
is recommended that ALRCK still be used to synchronized the counter, but on a
less frequent basis.