Serial Host Interface (SHI, SHI_1)
Symphony DSP56724/DSP56725 Multi-Core Audio Processors, Rev. 0
Freescale Semiconductor
10-19
•
Data valid—The state of the data line represents valid data when, after a start event, the data line
is stable for the duration of the high period of the clock signal. The data on the line may be changed
during the low period of the clock signal. There is one clock pulse per bit of data.
Figure 10-8. I
2
C Start and Stop Events
Each 8-bit word is followed by one acknowledge bit. This acknowledge bit is a high level put on the bus
by the transmitter when the master device generates an extra acknowledge-related clock pulse. A slave
receiver that is addressed must generate an acknowledge after each byte is received. Also, a master
receiver must generate an acknowledge after the reception of each byte that has been clocked out of the
slave transmitter. The acknowledging device must pull down the SDA line during the acknowledge clock
pulse, so that the SDA line is stable low during the high period of the acknowledge-related clock pulse (see
Figure 10-9. Acknowledgment on the I
2
C Bus
A device generating a signal is called a transmitter, and a device receiving a signal is called a receiver. A
device controlling a signal is called a master, and devices controlled by the master are called slaves. A
master receiver must signal an end-of-data to the slave transmitter by not generating an acknowledge on
the last byte clocked out of the slave device. In this case the transmitter must leave the data line high to
enable the master to generate the stop event. Handshaking may also be accomplished by using the clock
synchronizing mechanism. Slave devices can hold the SCL line low, after receiving and acknowledging a
byte, to force the master into a wait state until the slave device is ready for the next byte transfer. The SHI
supports this feature when operating as a master device, and waits until the slave device releases the SCL
line before proceeding with the data transfer.
S
P
AA0423
SCL
SDA
Start Event
Stop Event
S
1
2
8
9
AA0424
Data Output
by Receiver
Data Output
by Transmitter
SCL from
Master Device
Start Event
Clock Pulse for
Acknowledgement
Содержание Symphony DSP56724
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Страница 52: ...Symphony DSP56724 DSP56725 Multi Core Audio Processors Rev 0 2 30 Freescale Semiconductor Signal Descriptions ...
Страница 112: ...Symphony DSP56724 DSP56725 Multi Core Audio Processors Rev 0 7 12 Freescale Semiconductor Clock Generation Module CGM ...
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