AC4868 868 MHz Transceiver
User’s Manual
Americas: +1-800-492-2320 Option 3
12
Laird Technologies
Europe: +44-1628-858-940
Hong Kong: +852 2923 0610
www.lairdtech.com/ramp
S
ERIAL
I
NTERFACE
In order for the OEM Host and a transceiver to communicate over the serial interface they need to have the
same serial data rate. Refer to the following sections to ensure that the OEM Host data rate matches the serial
interface baud rate.
Serial Communications
The AC4868-250 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.
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 below.
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.
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 in the data and parity sum 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 below.
Figure 3: Even Parity Bit
Note: Enabling parity cuts throughput and the interface buffer in half.
