Freescale Semiconductor MCF52277 Reference Manual page 572

Synchronous Serial Interface (SSI)
TX, RX Sections
Synchronous
Synchronous
Synchronous
The transmit and receive sections of the SSI are only available in synchronous mode. In this mode, the
transmitter and the receiver use a common clock and frame synchronization signal. The
SSI_RCR[RXBIT0, RSHFD] bits can continue affecting shifting-in of received data in synchronous
mode. Continuous or gated clock mode can be selected. In continuous mode, the clock runs continuously.
In gated clock mode, the clock is only functioning during transmission.
Normal or network mode can also be selected. In normal mode, the SSI functions with one data word of
I/O per frame. In network mode, any number from two to thirty-two data words of I/O per frame can be
used. Network mode is typically used in star or ring time-division-multiplex networks with other
processors or codecs, allowing interface to time division multiplexed networks without additional logic.
Use of the gated clock is not allowed in network mode. These distinctions result in the basic operating
modes that allow the SSI to communicate with a wide variety of devices.
Typically, normal and network modes are used in a periodic manner, where data transfers at regular
intervals, such as at the sampling rate of an external codec. Both modes use the concept of a frame. The
beginning of the frame is marked with a frame sync when programmed with continuous clock. The
SSI_CCR[DC] bits determine length of the frame, depending on whether data is being transmitted or
received.
The number of words transferred per frame depends on the mode of the SSI. In normal mode, one data
word transfers per frame. In network mode, the frame divides into two to 32 time slots. In each time slot,
one data word is optionally transferred.
Apart from the above basic modes of operation, SSI supports the following modes that require some
specific programming:
2
• I S mode
• AC97 mode
— AC97 fixed mode
— AC97 variable mode
2
In non-I S slave modes (external frame sync), the SSI's programmed word length setting should be equal
to the word length setting of the master. In I
be lesser than or equal to the word length setting of the I
In slave modes, the SSI's programmed frame length setting (DC bits) can be lesser than or equal to the
frame length setting of the master (external codec).
See Section 25.4.1, "Detailed Operating Mode Descriptions,"
25-4
Table 25-1. SSI Operating Modes
Serial Clock Mode
Continuous Normal
Continuous Network
Gated Normal
2
S slave mode, the SSI's programmed word length setting can
MCF52277 Reference Manual, Rev. 1
Typical Application
Multiple synchronous codecs
TDM codec or DSP network
SPI-type devices; DSP to MCU
2
S master (external codec).
for more details on the above modes.
Freescale Semiconductor