cs4924 Cirrus Logic, Inc., cs4924 Datasheet - Page 37

• Manufacturer Part Number: cs4924
• Description: Multi-channel Digital Audio Decoders Logic
• Manufacturer: Cirrus Logic, Inc.

6.3.1 SPI Write
When writing to the device in SPI, the same
protocol can be used for sending a byte, a word or
an entire download image as long as transfers occur
on byte boundaries. Figure 19 illustrates the
relative timing necessary for a three byte transfer to
the CS492X. The host initiates an SPI write by
driving CS low, followed by a 7-bit address and the
read/write bit set low to indicate a write. The
CS4923/4/5/6/7/8/9 internal 7-bit address is
initially assigned to 000 0000b following a reset.
The 7-bit address sent to the CS492X must match
its internal address or the incoming data will be
ignored. Address checking can be changed (either
disabled or an actual address change) if desired.
Address checking configuration is documented in
the hardware configuration section of the
CS4923/4/5/6/7/8/9 Hardware User’s guide.
Data should be shifted into the CS492X most
significant bit first with data being valid at the
rising edge of SCCLK. It should be noted that data
is internally transferred to the DSP on the falling
edge of the eighth SCCLK after the eighth data bit
of a byte. For this reason SCCLK must transition
from high to low on the last bit of each byte or a
loss of data will occur. If this final transfer of
SCCLK does not occur the final byte will be lost
and successful communication will not be possible.
6.3.2 SPI Read
The CS4923/4/5/6/7/8/9 will always indicate that it
has data to be read by asserting the INTREQ line
low. The host must recognize the request and start
a read transaction with the CS492X. The same
protocol will be used whether reading a byte or
multiple bytes. Figure 19 also illustrates the
relative timing of a three byte SPI read.
DS262F2
The host initiates an SPI read by driving CS low,
followed by a 7-bit address and the read/write bit
set high to indicate a read. The CS492X internal 7-
bit address is initially assigned to 000 0000b
following a reset. The 7-bit address sent to the
CS492X must match its internal address or the
incoming data will be ignored. Address checking
can be disabled or the actual address can be
changed
configuration is documented in the hardware
configuration section of the CS4923/4/5/6/7/8/9
Hardware User’s guide.
After the address byte the host should clock data
out of the device one byte at a time until INTREQ
is no longer low. The host shifts data using the
rising edge of SCCLK. The data is valid on the
rising edge of SCCLK and transitions occur on the
falling edge. In SPI mode, the INTREQ pin is
deasserted immediately following the rising edge
of the second-to-last data bit of the current byte
being transferred if there is no more data to be read.
The INTREQ pin is guaranteed to stay deasserted
(high) until the rising edge of SCCLK for the last
data bit.
If there is more data to be read from the DSP before
the rising edge of SCCLK for the second-to-last
data bit, then INTREQ remains asserted low.
Immediately following the falling edge of SCCLK
for the last data bit of the current byte, the next data
byte loads into the internal serial shift register. The
host should continue to read this new byte. It is
important to note that once the data is in the shift
register, clocks on the SCCLK line shift the data
bits out of the shift register as long as CS is low.
For a thorough look at SPI communication and
critical additional comments on INTREQ behavior
reference the CS4923/4/5/6/7/8/9 Hardware User’s
Guide.
if
desired.
CS4923/4/5/6/7/8/9
Address
checking
37