Freescale Semiconductor DSP56366 - Manual (Page 195)

Operating Modes
DSP56366 24-Bit Digital Signal Processor User Manual, Rev. 4
Freescale Semiconductor 8-45
8. ESAI Transmit Data
Occurs when the transmit interrupt is enabled (TIE=1), at least one of the enabled transmit data
registers is empty (TDE=1), no exception has occurred (TUE=0 or TEIE=0), and no even slot
interrupt has occurred (TEDE=0 or TEDIE=0).
Writing to all the TX registers of the enabled transmitters, or to the TSR clears this interrupt
request.
8.4.4 Operating Modes – Normal, Network, and On-Demand
The ESAI has three basic operating modes and many data/operation formats.
8.4.4.1 Normal/Network/On-Demand Mode Selection
Selecting between the normal mode and network mode is accomplished by clearing or setting the
TMOD0-TMOD1 bits in the TCR register for the transmitter section, and in the RMOD0-RMOD1 bits in
the RCR register for the receiver section.
For normal mode, the ESAI functions with one data word of I/O per frame (per enabled transmitter or
receiver). The normal mode is typically used to transfer data to/from a single device.
For the network mode, 2 to 32 time slots per frame may be selected. During each frame, 0 to 32 data words
of I/O may be received/transmitted. In either case, the transfers are periodic. The frame sync signal
indicates the first time slot in the frame. Network mode is typically used in time division multiplexed
(TDM) networks of codecs, DSPs with multiple words per frame, or multi-channel devices.
Selecting the network mode and setting the frame rate divider to zero (DC=00000) selects the on-demand
mode. This special case does not generate a periodic frame sync. A frame sync pulse is generated only
when data is available to transmit. The on-demand mode requires that the transmit frame sync be internal
(output) and the receive frame sync be external (input). Therefore, for simplex operation, the synchronous
mode could be used; however, for full-duplex operation, the asynchronous mode must be used. Data
transmission that is data driven is enabled by writing data into each TX. Although the ESAI is double
buffered, only one word can be written to each TX, even if the transmit shift register is empty. The receive
and transmit interrupts function as usual using TDE and RDF; however, transmit underruns are impossible
for on-demand transmission and are disabled.
8.4.4.2 Synchronous/Asynchronous Operating Modes
The transmit and receive sections of the ESAI may be synchronous or asynchronous – i.e., the transmitter
and receiver sections may use common clock and synchronization signals (synchronous operating mode),
or they may have their own separate clock and sync signals (asynchronous operating mode). The SYN bit
in the SAICR register selects synchronous or asynchronous operation. Since the ESAI is designed to
operate either synchronously or asynchronously, separate receive and transmit interrupts are provided.
When SYN is cleared, the ESAI transmitter and receiver clocks and frame sync sources are independent.
If SYN is set, the ESAI transmitter and receiver clocks and frame sync come from the transmitter section
(either external or internal sources).