AT75C Datasheet, PDF (163/171 Pages) ATMEL Corporation – Smart Internet Appliance Processor (SIAP)

Codec Interface
Operation
Master Mode
Slave Mode
AT75C DSP Subsystem
This section describes the standard operation of the codec interface, reviewing the dif-
ferent modes available.
The external codec device and the codec interface are said to be in the master mode
when the external codec device delivers the serial clock (SCLK) and the frame sync
(FS) information. This mode allows the AT75C and the codec device to be fully asyn-
chronous (i.e., with separate clock sources) because the synchronization is maintained
by the SCLK and FS signals. This insures that the codec device will deliver a new sam-
ple when it is available and will accept a new sample when it is able to, according to its
own conversion timing.
The master mode is recommended because it leads to robust synchronization between
the codec device and the application software and does not require accurate timing
calculations.
Figure 14 illustrates an AT75C and a codec device connection in master mode.
Figure 14. Connection of a Codec Device in Master Mode
Asynchronous
Clocks
AT75C310
SCLK
FS
SDO
SDI
Codec Device
SCLK
FS
SDI
SDO
Note that programming FS and SCLK to be in opposite directions is not recommended.
In slave mode the serial clock (SCLK) and the frame sync (FS) signals are delivered by
the AT75C. To achieve data synchronization between the AT75C and the codec device,
the following rules must be respected:
• The AT75C system clock and the codec device clock must be kept in sync.
• The SCLK generator in the AT75C must be programmed to generate a serial clock
with a frequency compatible with the codec device.
• Because the AT75C initiates the transfers, the FS generator must be accurately
programmed so that data are exchanged when the codec device is ready to
accept/deliver them.
The slave mode operation is not recommended in a typical design because it has strong
requirements on the overall system clock strategy and requires fine tuning of the AT75C
codec interface. However, it allows the accommodation of some industry-standard
codec devices provided that the rules described above are followed.
Figure 15 illustrates an AT75C and a codec device connection in slave mode.
1368C–INTAP–08/02
163