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It is important to note that the TR-XXX-SC-PA does not encode or packetize the

data in any manner. This transparency eliminates the issues of variable latency

common to traditional radio modems and gives the designer tremendous

flexibility in the structure of protocol. A drawback to this approach is that the

performance and reliability of the link is in part determined by the quality of

external software and hardware.

The SC-PA is a half-duplex transceiver, meaning it can only act as a transmitter

or a receiver at any given time, but never both. Designing a system with a half-

duplex transceiver can be a bit challenging because of the timing requirements

when shifting between transmit and receive modes. A typical systems operation

would be similar to the following:

1)

Switch to transmit mode

The transceiver is placed in transmit mode by bringing TXEN high and RXEN

low. The PDN pin must be open or pulled to VCC. Once the transceiver is placed

in transmit mode, the synthesizer will begin trying to lock.

2)

Wait for transmitter to stabilize

This step is necessary to allow the transmitter time to lock and stabilize. Several

options are available during this time. The designer might choose to set a fixed

delay equal to the worst-case stabilization time before sending data. Another

method would be to send data immediately, knowing that it would not be valid

until the transmitter had stabilized. Depending on packet size, the latter method

may achieve faster turnaround times but would require more care from a protocol

standpoint.

3)

Transmit a packet

Structuring the data to be sent into small packets is highly recommended. That

way, errors can be managed easily without affecting large amounts of data.

Packets should be transmitted so that there is no space between bytes. When

using a UART the following packet format is generally followed:

[ uart sync byte ] [ start byte ] [ data packet ]

The UART Sync Byte is used to ensure that the start-bit for the start byte will be

accurately detected. It is a single byte with a value of 255 (0FF hex).

A Start Byte often follows the Sync Byte to intelligently qualify the Data Packet

which will follow. Detection of the Start Byte would be performed by the computer

or microcontroller connected to the transceiver.

4)

Switch to receive mode

The transceiver is placed in receive mode by bringing RXEN high and TXEN low.

The PDN pin must be open or pulled to VCC. Once the transceiver is placed in

receive mode, the PLL will begin trying to lock.

5)

Wait for receiver to stabilize

This step is necessary to allow the receiver time to stabilize. When the PLL is

locked and the data slicer is stable, the transceiver is ready to receive valid data.

During the settling time the receiver output may produce scraps of data; however,

the data can only be considered reliable once the settling time has passed.