Data Sheet

AC4790
Datasheet
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5 SERIAL INTERFACE
In order for the OEM host and a transceiver to communicate over the serial interface they must be set to the same serial data
rate. Refer to the following sections to ensure that the OEM host data rate matches the serial interface baud rate.
5.1 Serial Communications
The AC4790 is a TTL device which can be interfaced to a compatible UART (microcontroller) or level translator to allow
connection to serial devices. UART stands for Universal Asynchronous Receiver Transmitter and its main function is to
transmit or receive serial data.
5.2 Asynchronous Operation
Since there is no separate clock in asynchronous operation, the receiver needs a method of synchronizing with the transmitter.
This is achieved by having a fixed baud rate and by using START and STOP bits. A typical asynchronous mode signal is
shown in Figure 2: Asynchronous Mode Signal.
Figure 2: Asynchronous Mode Signal
The UART outputs and inputs logic-level signals on the Tx and Rx pins. The signal is High when no data is being transmitted
and goes Low when transmission begins.
The signal stays Low for the duration of the START bit and is followed by the data bits, LSB first. The STOP bit follows the last
data bit and is always High. After the STOP bit has completed, the START bit of the next transmission can occur.
5.3 Parity
A parity bit is used to provide error checking for a single bit error. When a single bit is used, parity can be either even or odd.
Even parity means that the number of ones (1) in the data and parity add up to an even number and vice-versa. The ninth data
bit can be used as a parity bit if the data format requires eight data bits and a parity bit as shown in Figure 3. See Table 5 for
supported serial data formats.
Figure 3: Even Parity Bit
Note: Enabling parity cuts throughput and the interface buffer in half.