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AS3977

Data Sheet - D e t a i l e d S y s t e m D e s c r i p t i o n

8.8 SDI / Control Interface

This interface enables a serial and synchronous communication between external microcontroller and AS3977. Data can be written to and read

out from AS3977. Additionally, it facilitates the transmission of TX-data. The rising edge on the SDI enable signal (transition to the active state),

while the device is in Power Down Mode has various effects on the circuit:

- It wakes up the crystal oscillator (this takes maximum 1.5 ms with the specified Crystal parameters)

- It sets the transfer and sampling edge of the AS3977 SDI data signal.

- It activates the Micro Controller clock output depending on the register setting and the value of the data signal.

Thus, the wakeup event through the SDI interface determines the basic communication between AS3977 and the microcontroller. In addition it

takes some time to have a stable crystal oscillator clock available. Therefore all functions that require a stable crystal oscillator clock are not

immediately available after the wakeup.

8.9 Baud Rate Generator

This module generates two clocks; one used for the microcontroller (MCCLK) and one as baud rate clock with 50% duty cycle. The baud rate

clock is used by the microcontroller to properly synchronize the provided data during transmission with the internal Manchester coder.

The baud rate generator maintains the behavior of MCCLK and keeps it properly synchronized to the TX data clock. For example, a missing

synchronization can occur when clock settings are changed by an asynchronous event like SDI programming or when a new transmission starts.

The Baud rate generator offers different types of data outputs: one fully asynchronous, one synchronous and one synchronous but Manchester

coded. By means of AS3977 command control Byte, any of the three different output data types can be selected.