ISD3900
Publication Release Date: Dec 10, 2013
- 70 -
Revision 1.5
FIFO
SPI OUT
SPI IN
UP
SAMPLE
FILTER
DOWN
SAMPLE
FILTER
DECOMPRESSOR
COMPRESSOR
MEMORY
CONTROL
Figure 13-4 Feed-through SPI
The RDY/BSYB pin will go low whenever the internal FIFO is empty. If no path or playback operation
is set up then RDY/BSYB pin will be low until command is terminated. If RDY/BSYB is ignored then an
OVF_ERR interrupt is generated.
13.1.12 SPI Send Compressed Data to Decode
SPI_SND_DEC
Byte Sequence:
Host controller
0xC0
D0[7:0]
D1[7:0]
….
Dn[7:0]
ISD3900
Status
Byte
Description:
Write compressed audio data via SPI interface.
Interrupt
Generation:
OVF_ERR if RDY/BSYB violated.
This command allows the user to send compressed audio data, in a byte formatted bit stream, down
the SPI interface to the de-compressor and signal path. Before execution of command (1) a valid
signal path must be set up. Valid paths are similar to a standard playback. (2) Multiple SPI_SND_DEC
commands can be issued to send data to the ISD3900. (3) To finish decoding a STOP command is
sent and device will respond with a CMD_FIN interrupt. RDY/BSYB pin will handshake dataflow if
device cannot accept any further data for decompression. If host cannot keep up with data rate audio
output will be corrupted.