9XTend-PKG-R™ RS-232/485 RF Modem

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9XTend‐PKG‐R RS‐232/485 RF Modem – Product Manual v1.2.43.2. Modes of OperationXTend RF Modems operate in five modes.Figure 3‐03. Modes of OperationThe RF modem can only be in one mode at a time.3.2.1. Idle ModeWhen not receiving or transmitting data, the modem is in Idle Mode. The modem uses the sameamount of power in Idle Mode as it does in Receive Mode.The modem shifts into the other modes of operation under the following conditions:• Serial data is received in the DI Buffer (Transmit Mode)• Valid RF data is received through the antenna (Receive Mode)• Command Mode Sequence is issued (Command Mode)• Sleep Mode condition is met (Sleep Mode)The modem automatically transitions to Idle Mode after responding to these conditions.3.2.2. Transmit ModeWhen the first byte of serial data is received from the host in the DI buffer, the modem attemptsto shift to Transmit Mode and initiate an RF connection with other modems. After transmission isfinished, the modem returns to Idle Mode.RF transmission begins after either of the following criteria is met:1. RB bytes have been received by the host and are pending for RF transmission.[RB (Packetization Threshold) Command]2. At least one character has been received by the host and is pending for RF transmission, andRO character times of silence have been observed on the host.[RO (Packetization Timeout) Command]Figure 3‐04. Transmit Mode Data FlowThe character timeout trigger canbe disabled by setting RO to zero.In this case, transmission will notbegin until RB bytes have beenreceived and are pending for RFtransmission. The RB parametermay be set to any value between 1and the RF packet size (PK),inclusive. Note that transition toTransmit Mode cannot take placeduring RF reception; the RFreception must complete beforethe modem can transition intoTransmit Mode.© 2005 MaxStream, Inc. Confidential and Proprietary 14
9XTend‐PKG‐R RS‐232/485 RF Modem – Product Manual v1.2.4After either of the RB and RO conditions are met, the modem then initializes a communicationschannel. Serial data in the DI buffer is grouped into RF packets (up to 2048 bytes in each packet- refer to PK (Maximum RF Packet Size) Command), converted to RF data and then is transmittedover-the-air until the DI buffer is empty.Channel initialization is the process of sending an RF initializer that synchronizes receivingmodems with the transmitting modem. During channel initialization, incoming serial dataaccumulates in the DI buffer.RF data, which includes the payload data, follows the RF initializer. The payload includes up tothe maximum packet size (PK Command) bytes. As the TX modem nears the end of thetransmission, it inspects the DI buffer to see if more data exists to be transmitted. This could bethe case if more than PK bytes were originally pending in the DI buffer or if more bytes arrivedfrom the host during transmission. If more data is pending, the transmitting modem instructs alllistening modems that a subsequent packet is coming. Receiving modems move to the newfrequency and listen for the subsequent packet.Refer to the RF Communication Options [p41] section for information and state diagrams thatillustrate channel initialization and the sequence of events that follow.RF PacketFigure 3‐05. RF Packet Components* When streaming multiple RF packets, the RF Initializer is only sent in front of the first packet.RF InitializerAn RF initializer is sent each time a new connection sequence begins. The RF initializer containschannel information that notifies receiving modems of information such as the hopping patternused by the transmitting modem. Channel initialization takes 5 ms at the 115k RF data rate and54 ms at the 9600 RF data rate. The first transmission always sends an RF initializer.An RF initializer can be of various lengths depending on the amount of time determined to berequired to prepare a receiving modem. For example, a wake-up initializer is a type of RFinitializer used to wake remote modems from Sleep Mode (Refer to the FH, LH, HT and SMCommands for more information). The length of the wake-up initializer should be longer than thelength of time remote modems are in cyclic sleep.HeaderThe header contains network addressing information that filters incoming RF data. The receivingmodem checks for matching a Hopping Channel, VID and Destination Address. Data that does notpass through all three network security layers is discarded.Figure 3‐06. Network Layers Contained in the Header© 2005 MaxStream, Inc. Confidential and Proprietary 15
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9XTend-PKG-R™ RS-232/485 RF Modem

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