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Barnett Engineering B1474 Operation Manual Download Page 17

6  IN DI CA TORS

The LED indicators on the front case are used to indicate modem status:

RUN

Power is on the modem.

BUSY

The modem is waiting to transmit but is held back by the squelch detector.

RTS

Request To Send from the computer is present or characters have been

re ceived into the buffer.

CTS

Clear To Send is active.

CD

Carrier is detected on the incoming channel.

RXD

On when a mark is received and off when a space is received.

TXD

On when a mark is transmitted.

The LEDs may be dis abled to con serve power by set ting SW1.1 off.

B1474

BARNETT EN GI NEERING LTD.

PAGE  16

Summary of Contents for B1474

Page 1: ...RADIO MODEM B1474 OPERATION MANUAL April 1998 Manual Revision 4 1 for Version 2 1 Hardware ...

Page 2: ...3 2 SPECIFICATIONS 5 3 NOTATION 7 4 OPERATION 8 5 SETUP PROCEDURES 12 6 INDICATORS 16 7 CONFIGURATION 17 8 CONNECTIONS 19 9 BOARD LAYOUT 20 10 WARRANTY STATEMENT 21 11 APPENDIX A OPERATION WITH A GE TRUNKING SYSTEM 22 B1474 BARNETT ENGINEERING LTD PAGE 1 ...

Page 3: ...hich are designed to provide reasonable protection against interference when operated in a commercial environment Operation of this equipment in a residential area is likely to cause interference in which case the user at his own expense will be required to take whatever measures may be required to correct the interference This device was tested using a shielded cable connected to the data port Th...

Page 4: ...ble in the B1474 are Hardware or Software Handshaking Either RTS and CTS hardware signals or software XON and XOFF characters can be used to pause the transmitting station while waiting for the radio system to respond If short data streams are to be sent full data buffering may be used to render the radio system transparent RTS CTS Delay This adjustable delay allows the radio to warm up before dat...

Page 5: ...Indicators Modem status condition is indicated by front panel LEDs The LEDs may be disabled to conserve power B1474 BARNETT ENGINEERING LTD PAGE 4 ...

Page 6: ... BUSY Receive Audio Single ended AC coupled 30 dBm to 0 dBm Transmit Audio Single ended AC coupled 20 dBm to 0 dBm Squelch Detection Single ended 1M ohm impedance DC coupled detection range 0 to 10 volts polarity is DIP switch selectable PTT Closure to ground for active 0 5 A 50 volts max 4 Wire Receive Balanced 600 ohm impedance 30 dBm to 0 dBm operates full or half duplex 4 Wire Transmit Balance...

Page 7: ... ensure squelch tail noise doesn t interfere with data at the receiving terminal Handshaking Specifies the type of flow control used 2 4 Wire Selects 2 or 4 wire cable operation LED Control Disables LEDs to save power Equalization Full Half Duplex B1474 BARNETT ENGINEERING LTD PAGE 6 ...

Page 8: ... Commission GND Ground PTT Push To Talk RFCTS RF Clear To Send used in trunking systems only RTS Request To Send SQL Squelch SW1 8 This signifies a DIP switch The given example describes the eighth position on DIP switch number one XOFF ASCII 13h sent by a receiving station instructing the sending station to halt any transmission XON ASCII 11h sent by a receiving station instructing the sending st...

Page 9: ... detect delay at the receiving end The modem at the receiving end senses carrier on the line and asserts its CD The received data is muted for 5 or 50 msec to ensure that transients do not affect the received data At the sending end once the RTS CTS delay timer has expired the modem returns a CTS to the sending computer Data is transmitted any format may be used Once all the data has been transmit...

Page 10: ...B1474 BARNETT ENGINEERING LTD PAGE 9 FIGURE 1 MODEM TIMING USING RTS AND CTS ...

Page 11: ... delay at the receiving end The modem at the receiving end senses carrier on the line and asserts its CD The received data is muted for 5 or 50 msec to ensure that transients do not affect the received data At the sending end once the RTS CTS delay timer has expired data is transmitted The sending modem s PTT drop delay timer is started at the end of the last transmitted character Once the PTT dro...

Page 12: ... delay timer has expired the modem releases the radio transmitter and returns to receive mode This configuration can buffer 500 msec worth of characters To prevent internal data buffer overflow it is important that the radio system will be available within 500 msec RTS CTS delay plus maximum channel busy time or the maximum amount of buffered data be less than 50 characters For no handshaking buff...

Page 13: ...e for a cable interface For a single ended radio interface connect P1 3 to the transmit line of the radio and P1 6 to the receive line Connecting the receive input to an unsquelched source in the radio will result in extraneous characters at the data port unless the squelch detector is set properly PTT The B1474 provides an open collector driver for the radio PTT at P1 10 Squelch The radio s recei...

Page 14: ...RTS CTS delay specifies the amount of data which will be buffered Set DIP switches SW1 2 SW1 3 and SW1 4 for the desired delay from 20 to 1000 msec as specified in Section 7 Configuration PTT Drop Delay When transmission is no longer requested by the sending computer a selectable delay is inserted before the PTT on the radio is released This delay prevents the squelch tail at the receiving radio f...

Page 15: ...hardware handshaking or conventional radios Transmit Level To adjust the output level of the modem to between 0 and 20 dBm set DIP switches SW2 1 SW2 2 and SW2 3 as specified Section 7 Configuration The output levels given are referenced into 600 ohms Should the output be driven into a high impedance the level will be approximately 6 dB higher than expected If a high level is required into a singl...

Page 16: ...onnector and set SW3 2 OFF If XON XOFF control software handshaking or no handshaking with full buffering is desired set SW3 2 ON and remove connections from the RTS and CTS positions in the DB 25S connector 2 4 Wire Set SW3 3 and SW3 4 OFF if 4 wire communications are used Set SW3 3 and SW3 4 ON if 2 wire communications are used If a 2 wire circuit is used the modem will only operate half duplex ...

Page 17: ...detector RTS Request To Send from the computer is present or characters have been received into the buffer CTS Clear To Send is active CD Carrier is detected on the incoming channel RXD On when a mark is received and off when a space is received TXD On when a mark is transmitted The LEDs may be disabled to conserve power by setting SW1 1 off B1474 BARNETT ENGINEERING LTD PAGE 16 ...

Page 18: ...IVE TRUNKING ONLY NO XON XOFF X USE XON XOFF 8 XON XOFF LOW CHANNEL FREE X HIGH CHANNEL FREE 9 SQUELCH POLARITY SWITCH 2 Bal X 4 2 3 0 8 X 6 X 10 8 X 12 10 X X 14 X 16 X 20 X 20 X X 24 2 TX LEVEL INTO 600 OHMS Radio dBm 4 X 6 1 MODE 3 DUPLEX 8 FULL DUPLEX X HALF DUPLEX RX GAIN 5 dB 0 X 10 MODE 1 EQUALIZATION 6 NO RECEIVE EQUALIZATION X RECEIVE EQUALIZATION MODE 2 CD DELAY 7 CD DELAY 5 msec X CD DE...

Page 19: ...B1474 BARNETT ENGINEERING LTD PAGE 18 BUFFER USE RTS CTS CONTROL X USE BUFFER 2 SWITCH 3 RTS ON 4 WIRE CABLE X 2 WIRE CABLE 4 RTS ON EXTERNAL RTS X RTS ON AT ALL TIMES 1 X 3 ...

Page 20: ... SQL PTT TRANSMIT OUTPUT SINGLE ENDED TRANSMIT OUTPUT BALANCED RECEIVE INPUT BALANCED SQUELCH DETECTOR INPUT RECEIVE INPUT SINGLE ENDED P3 DIGITAL P1 AUDIO 8 PIN 7 5 4 3 2 1 10 SYMBOL GND TXD RXD RTS CTS SIG GND CD CARRIER DETECT RECEIVE DATA CLEAR TO SEND SIGNAL GROUND REQUEST TO SEND TRANSMIT DATA CHASSIS GROUND PUSH TO TALK OUTPUT 8 CONNECTIONS ...

Page 21: ...9 BOARD LAYOUT B1474 BARNETT ENGINEERING LTD PAGE 20 ...

Page 22: ...he purchase price at Barnett Engineering Ltd s option after return of such equipment by the buyer to Barnett Engineering Ltd Shipment to Barnett Engineering Ltd s facility shall be borne on account of the buyer 1 Consequential Damages Barnett Engineering Ltd shall not be liable for any incidental or consequential damages incurred as a result of any defect in any equipment sold hereunder and Barnet...

Page 23: ... a trunked channel and transmitting the sending computer s data using hardware RTS CTS handshaking is described below Refer to Figure 2 for an illustration of the timing relationships 1 The sending computer asserts its Request to Send RTS causing the modem to key the radio and wait for a channel to be assigned 2 When the channel is assigned the trunking radio returns RF Clear to Send RFCTS to the ...

Page 24: ...B1474 BARNETT ENGINEERING LTD PAGE 23 FIGURE 2 MODEM TIMING FOR A GE MARC V TRUNKING SYSTEM USING RTS CTS HANDSHAKING ...

Page 25: ... channel sets its RTS CTS delay timer The receiving modem senses carrier on the line and asserts its CD The received data is muted for 5 or 50 msec to ensure that transients do not affect the received data After the RTS CTS delay timer has expired data is transmitted Whenever the modem receives a character from the sending device or transmits any buf fered character it restarts the PTT drop delay ...

Page 26: ...senses carrier on the line and asserts its CD The received data is muted for 5 or 50 msec to ensure that transients do not affect the received data After the RTS CTS delay timer has expired data is transmitted Receipt of any character or transmission of any buffered character restarts the modem s PTT drop delay timer Once the modem stops receiving characters and the PTT drop delay timer expires th...

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