Jenn-Air 1300, 1892 manual Data Transfer Modes, RS232 Data Handling, Receive-to-Transmit Turnround

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3.3Data Transfer Modes

In FEC mode every byte of the data, including the "end-of-file" string is scrambled within the modem to ensure that the error correction mechanism operates over non-consecutive bits in the data stream. The frame sync pattern is not scrambled.

In non-FEC (High Speed) mode the data is scrambled to minimise problems that could occur with many consecutive 1's or 0's in the input data stream.

3.4RS232 Data Handling

The over-air data rate is faster than the input data rate because only the 8 data bits of the input character of 11 bits are transmitted. To ensure that no data is lost at the output, and for the modem to transmit the data in one continuous packet it is essential that the input and output data rates are set to at least 2 x the over-air-baud rate. The default over-air baud rate for this modem working in a 12.5kHz channel is 9600 baud. For this set the input and output RS232 data rates to 19,200. For a 25kHz channel, with an over- air baud rate of 19,200, set the data rates to 38,400 baud.

Some applications running under the Windows™ operating system output the data with gaps between single or groups of characters. In some cases this can reduce the character rate below the over-air data rate. When this occurs, the system will assume that the input data has finished and will turn the transmitter off when the input data buffer is empty.

If more characters are input to the modem while the transmitter is being turned off, the transmit process will re-start. This will appear as bursts of RF close together. At the receive end, the timing of the data will change as there will be gaps in the received data stream.

This mode of operation ensures that small data packets are transmitted in as short a time as possible to reduce the on-air time to a minimum.

3.5Receive-to-Transmit Turnround

After the last character of a packet of data is output from the receiver, the receive system is still processing the “end-of-packet” data. This takes ~5ms when in non-FEC mode and ~10ms in FEC mode. During this period the processor does not accept any input data. The figures apply for default settings: 19,200 baud rate and 4800 symbol/sec over-air baud rate

Hermes Operator Note

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Contents Tel +44 0 118 981 Fax +44 0 118 981 Specialist RF DesignsLattice House Baughurst Basingstoke UK RG26 5LP Handshaking Operation During Transmit and Receive Table Of ContentsReceived Signal Strength Indication Rssi AT S156 List of Figures List of TablesIntroduction Pin No Function RS232 ConnectorConnections & Indications Front Panel Indications Power ConnectorRF Connector Modem Operation IntroductionReceive-to-Transmit Turnround Data Transfer ModesRS232 Data Handling MAX Time msDescription Okcrlf List of CommandsCommand Mode Command Syntax ErrorcrlfBaud Rate AT B0 Parity ATB1Format Mode AT F AT F?CRLFRXX, Dxxxcrlf Engineering Test Modes ATOK Crlf Command Mode Guard Time AT S154 Software Version Information ATATI9CRLF Centre Radio Frequency AT S155Rssi Level Level at RF Input dBm ±2dB Radio Channel AT S157 Data Quality AT S158Squelch AT S159 Squelch Level Level at RF InputTransmission Power AT S160 Output Power for 1W G-MAX Output Power for 2W G-MAXPower Level Output Power DBm Tolerance Nominal Level NominalChannel Step Size AT S161 Test Message Period AT S162Over-Air Symbol Rate AT S163 Note engineering function only Preamble Period AT S165 Note engineering function onlyInvert Symbol AT S167 Frame Synch Tolerance AT S166 Note engineering function onlySquelch Delay AT S168 Restore defaults AT &Y8 Radio Frequency AT &FSave parameters AT &W AT &WCRLFDisplay parameters ATT? ATT?CRLFDo not enter unless you wish to carry out a code load Ppppppppppppppppppppppppppppppppppppppppppppppppppppp Hardware Specification RS232 Port ParametersRadio Specifications Parameter Max SXn50Mechanical Specification EnclosuresFront View of Casting Vibration Specifications Operating conditionsType Approvals EMC