Cirrus Logic CS4953xx - Manual (Page 43)

3-11 Copyright 2010 Cirrus Logic, Inc. DS732UM10
I2C Port
CS4953xx Hardware User’s Manual
3.3.3.5 I 2 C Read Procedure
1. An I
2
C read transaction is initiated by CS4953xx driving SCP1_IRQ low, signaling that it has data to
be read.
2. The master responds by sending an I
2
C Start condition which is SCP1_SDA going low while
SCP1_CLK is held high.
3. This is followed by a 7-bit address and the read/write bit set high for a read. So, the master should
send 0x81. The 0x81 byte represents the 7-bit I
2
C address 1000000b, and the least significant bit set
to ‘1’, designates a read.
4. After the address byte, the master must release the data line and provide a ninth clock for the
CS4953xx DSP (slave) to acknowledge (ACK) receipt of the byte. The CS4953xx will drive the data
line low during the ninth clock to acknowledge. If for some reason CS4953xx does not acknowledge
(NACK), it means that the communications channel has been corrupted and the CS4953xx should be
re-booted. A NACK should never happen here.
5. The data is ready to be clocked out on the SCP1_SDA line at this point. Data clocked out by the host
is valid on the rising edge of SCP1_CLK and data transitions occur just after the falling edge of
SCP1_CLK.
6. After the CS4953xx has written the byte to the master on the SCP1_SDA line, it will release the
SCP1_SDA line. If the master has more bytes in the 4-byte word to read, then proceed to Step 7. If
the master is finished reading all bytes of the 4-byte word, then proceed to Step 8.
7. The master should drive the SCP1_SDA line low for the 9
th
SCP1_CLK clock to acknowledge (ACK)
that the byte was received from the CS4953xx. The master should then return to Step 5 to read
another byte of the 4-byte word.
8. If SCP1_IRQ is still low after reading a 4-byte word, proceed to Step 7. If SCP1_IRQ has risen,
proceed to Step 9. See Section 3.4.3.5 on page 3-21 for an in-depth explanation of SCP1_IRQ.
9. The master should let the SCP1_SDA line stay high for the 9th SCP1_CLK clock as a no-
acknowledge (NACK) to CS4953xx. This, followed by an I
2
C stop condition (SCP1_SDA driven high,
while SCP1_CLK is high) signals an end of read to CS4953xx.