Specifications

Operation 3
3.0 Operation
There are various operating states associated with the operation of the MaxStream XStream-PKG wireless modem.
The following sections describe the stages of operation.
3.1 Standby
When the radio is not transmitting or receiving, it is in standby mode and ready to receive data. From standby, the
radio can either transmit, if data is presented on the serial port; or receive, if data is presented over the air. The radio
returns to standby when data is no longer present either on the air or on the serial port, or if a receive error is
detected.
3.2 Transmitting
The MaxStream modem leaves standby mode when data is received by the serial port which then sends incoming
data through the air. Once in transmit mode, the modem starts to send buffered data. Data is sent in packets up to 64
bytes long. When the first byte is clocked into the transmit buffer, the modem begins the transition from standby to
transmit.The transition between standby mode and transmit mode take approximately 35 milliseconds (ms) which is
the approximate length of time it takes for the modem to receive serial port data and then transmit serial port data.
After the 35ms transition time, any bytes that are in the buffer are packetized and sent over the air.
The MaxStream XStream-PKG can buffer up to 132 characters before it must stop receiving characters. The
modem will de-assert the CTS flow control line when approximately 116 characters have been received to notify the
sending device to stop sending data. When the first packet has been transmitted if more bytes are in the buffer, they
are packetized and sent. If the buffer is empty, the modem transitions to standby mode.
3.3 Receiving
If data is present on the airwaves when the modem is in standby, it transitions to the receive mode. In receive mode
it receives a packet and transmits it out the serial port. Received packets are protected from data corruption by a
16-bit CRC. A packet is rejected and not sent out of the serial port if there is an error detected in the packet.
The modem stays in receive mode until no more data is detected or an error is detected. A modem in receiving mode
does not transmit data coming in to the serial port until after returning to standby mode. When there are gaps in
receiving data, the receiver automatically returns to standby mode. If the receiver has buffered data coming in to the
serial port, this data is sent after the modem returns to standby mode.