Jenn-Air 1892, 1300 manual Modem Operation, Introduction

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3MODEM OPERATION

3.1Introduction

The internal modem power supply system is turned on/off with the DTR input. The modem is ready after an initialisation period. The modem enters receive mode using the last set of configuration parameters (RF channel, squelch level etc).

The modem starts the transmit sequence after the first data byte is received from the RS232 port. The incoming data is stored while the transmitter is turned on and the preamble output. The start, stop and parity (if 8 bit data) are stripped off the input data stream and the data stored as 8 bits only.

The transmission is ended when the input buffer is empty. After the transmission is complete and the transmitter turned off, the modem switches back to receive mode. Transmission has priority over reception so the user has to check by means of the CD handshake line if the radio channel is free before inputting data.

The timing of the power, handshaking and data transfer is shown in Figure 1 for the G-MAX radio (running at 9600 baud over-air in a 12.5kHz channel) and for the SXn50 series of radios (running at 19,200 baud over-air in a 25kHz channel).

3.2Handshaking Operation During Transmit and Receive

The DTE must set the RTS input for the modem to accept data. The RTS input can be set continuously if no hardware handshake lines are available on the DTE. The CTS line must be monitored for data packets greater than 256 bytes to ensure that input buffer overflow does not occur. If the data input is not stopped within 10 characters from the point of buffer overflow, the input data will be discarded.

Handshaking is also required during the code loading.

The modem starts transmitting when the data is input, regardless of the state of the CD output. The DTE must check the CD output prior to data transmission. When the CD output is set this indicates that a RF signal is present at the antenna. This output is only active when the modem is not transmitting.

Hermes Operator Note

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Contents Lattice House Baughurst Basingstoke UK RG26 5LP Specialist RF DesignsTel +44 0 118 981 Fax +44 0 118 981 Received Signal Strength Indication Rssi AT S156 Table Of ContentsHandshaking Operation During Transmit and Receive List of Tables List of FiguresIntroduction Connections & Indications RS232 ConnectorPin No Function RF Connector Power ConnectorFront Panel Indications Introduction Modem OperationRS232 Data Handling Data Transfer ModesReceive-to-Transmit Turnround Description Time msMAX Command Mode List of CommandsOkcrlf Errorcrlf Command SyntaxParity ATB1 Baud Rate AT B0AT F?CRLF Format Mode AT FOK Crlf Engineering Test Modes ATRXX, Dxxxcrlf Centre Radio Frequency AT S155 Command Mode Guard Time AT S154Software Version Information AT ATI9CRLFRssi Level Level at RF Input dBm ±2dB Data Quality AT S158 Radio Channel AT S157Squelch Level Level at RF Input Squelch AT S159Level Nominal Transmission Power AT S160Output Power for 1W G-MAX Output Power for 2W G-MAX Power Level Output Power DBm Tolerance NominalTest Message Period AT S162 Channel Step Size AT S161Preamble Period AT S165 Note engineering function only Over-Air Symbol Rate AT S163 Note engineering function onlyFrame Synch Tolerance AT S166 Note engineering function only Invert Symbol AT S167Squelch Delay AT S168 AT &WCRLF Restore defaults AT &Y8Radio Frequency AT &F Save parameters AT &WATT?CRLF Display parameters ATT?Do not enter unless you wish to carry out a code load Ppppppppppppppppppppppppppppppppppppppppppppppppppppp RS232 Port Parameters Hardware SpecificationParameter Max SXn50 Radio SpecificationsEnclosures Mechanical SpecificationFront View of Casting EMC Vibration SpecificationsOperating conditions Type Approvals
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