Barnett Engineering B1474 User's Manual
Contents
1. PIN SYMBOL DESCRIPTION 1 V INPUT VOLTAGE 2 GND GROUND 3 TX RADIO TRANSMIT OUTPUT SINGLE ENDED 4 TX WL TRANSMIT OUTPUT BALANCED 6 RX RADIO RECEIVE INPUT SINGLE ENDED 7 RX WL 8 RX WL RECEIVE INPUT BALANCED 9 SQL SQUELCH DETECTOR INPUT 10 PTT PUSH TO TALK OUTPUT DIGITAL PIN SYMBOL 1 GND CHASSIS GROUND 2 TXD TRANSMIT DATA 3 RXD RECEIVE DATA 4 RTS REQUEST TO SEND 5 CTS CLEAR TO SEND 7 SIG GND SIGNAL GROUND 8 CD CARRIER DETECT B1474 BARNETT ENGINEERING LTD PAGE 19 9 BOARD LAYOUT 0 20 P J m r 000 lt 2000 i BARNETT ENGINEERING LTD PAGE 20 B1474 Barnett Engineering Product Warranty WARRANTY STATEMENT Barnett Engineering Ltd warrants that all equipment supplied shall be free from defects in material or workmanship at the time of delivery Such warranty shall extend from the time of delivery for a period of one year Buyer must provide written notice to Barnett Engineering Ltd within this prescribed warranty period for any defect If the defect is not the result of improper usage service maintenance or installation and the equipment has not been otherwise damaged or modified after delivery Barnett Engineering Ltd shall either replace or repair the defective part or parts of equipment or replace the equipment or refund the purchase price at Barnett Engineering Ltd s option after return of such equipment2. SW2 8 OFF operate half duplex set switch SW2 8 ON 2 wire circuit is used the modem will only operate half duplex RTS Control SW3 1 when ON will assert RTS continuously This causes PTT to be asserted and transmit tones to be generated The switch should be on for a no handshaking non buffered configuration The continuous RTS is also useful for testing purposes Buffer If hardware handshaking is desired connect the RTS and CTS signals to the DB 25S connector 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 4 Replace The Top Cover Place the top cover back onto the base and tighten the two center screws 5 Apply Voltage Apply the proper voltage to the unit If the LEDs are enabled the run lamp will illuminate indicating that power is available at the modem B1474 BARNETT ENGINEERING LTD PAGE 15 6 INDICATORS The LED indicators on the front case are used to indicate modem status RUN BUSY RTS 5 RXD TXD Power is on the modem The modem is waiting to transmit but is held back by the squelch detector Request To Send from the computer
3. 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 The unit must be operated using a shielded cable on the data line with the shield grounded B1474 BARNETT ENGINEERING LTD PAGE 2 1 INTRODUCTION The 1474 Radio Modem provides a reliable method of sending 1200 baud data signals over radio or cable facilities Digital information is converted to tone format for transmission over the communication channel Received tones are converted back to RS232 digital format Hardware handshaking using RTS and CTS signals allows the radio channel to be transparent to the connected equipment Warm up and power down delay times required by the radio do not affect the data signals Alternatively XON XOFF or data buffering may be used where hardware handshaking is not available The communication channel can be a single pair cable two pair cable or two way radio Conventional land mobile radio equipment can be used or if specified at time of order GE trunking radios may be used Power and audio signals are connected to compression terminals inside the modem the digital interface is through a DB 25S connector The B1474 requires 12 to 30 VDC negative ground and approximately 60 mA to operate Features available in the B1474 are Hardware or Software Handshaking Either RTS and CTS hardware signals or softwar
4. 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 drop delay timer has expired the modem releases the radio transmitter turns off the modem carrier 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 RTS CTS delay timer be set to a value less than 500 msec and that the computer respond to XOFF immediately For software handshaking set signaling on assert RTS continuous off and buffering on Do not connect hardware RTS and CTS Set RTS CTS delay and PTT drop delay as required No Handshaking Buffered Basic operation and timing with data buffering no handshaking are as follows The sending computer begins sending data Data format must be 8 bits no parity 1 stop bit e Upon detecting data the sending modem performs the following B1474 BARNETT ENGINEERING LTD PAGE 10 checks the channel if this feature is enabled If the channel is free it asserts its PTT to power up the radio s transmitter If the channel is busy it buffers the received data until the channel becomes free presents MARK tone carrier onto the channel sets its RTS CTS delay ti
5. is present or characters have been received into the buffer Clear To Send is active Carrier is detected on the incoming channel On when a mark is received and off when a space is received 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 7 CONFIGURATION SWITCH 1 LED CONTROL LEDS OFF LEDS ON RTS CTS DELAY 2 3 4 msec 20 35 50 100 200 300 500 1000 msec 0 10 20 50 75 100 250 XON XOFF 8 NO XON XOFF USE XON XOFF SQUELCH POLARITY LOW CHANNEL FREE HIGH CHANNEL FREE 9 SEND RECEIVE TRUNKING ONLY 10 __ PTT REGARDLESS OF RFCTS X PTT ONLY WITH RFCTS SWITCH 2 TX LEVEL INTO 600 OHMS Radio dBm Bal 4 6 2 8 4 10 6 12 8 14 10 20 24 20 RX GAIN 5 X qB 0 10 MODE 1 EQUALIZATION 6 X NO RECEIVE EQUALIZATION RECEIVE EQUALIZATION MODE 2 CD DELAY 7 CD DELAY 5 msec CD DELAY 50 msec MODE 3 DUPLEX FULL DUPLEX HALF DUPLEX B1474 BARNETT ENGINEERING LTD PAGE 17 SWITCH 3 RTS ON EXTERNAL RTS RTS ON AT ALL TIMES USE RTS CTS CONTROL USE BUFFER RTS ON 4 WIRE CABLE 2 WIRE CABLE B1474 BARNETT ENGINEERING LTD PAGE 18 8 CONNECTIONS
6. lost immediately on releasing PTT so the receiving computer can use the same channel to respond The receiving computer receives a Carrier Detect CD followed by the data some interval later B1474 BARNETT ENGINEERING LTD PAGE 22 FIGURE2 MODEM TIMING FOR A GE MARC V TRUNKING SYSTEM USING RTS CTS HANDSHAKING B1474 BARNETT ENGINEERING LTD PAGE 23 Software Handshaking Using XON XOFF Basic operation and timing using XON XOFF software handshaking in a trunking system is as follows The sending computer begins sending data The format must be 8 data bits no parity 1 stop bit e Upon detecting data the sending modem performs the following checks the channel If RFCTS has already been assigned the channel is available it as serts its to power up the radio s transmitter If the channel has not been assigned yet it sends XOFF to the sending computer and asserts PTT to obtain the channel When the channel gets assigned it sends XON to the computer and continues presents tones onto the 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 e After the RTS CTS delay timer has expired data is transmitted e Whenever the mod
7. sending computer does not understand these characters the switch must be OFF Squelch Polarity If the modem is connected to a radio the channel can be monitored for RF carrier SW1 9 is changed depending upon the polarity of the carrier operated switch COS signal If the COS goes high when carrier is present and low when the channel is free set SW1 9 OFF If the opposite occurs set SW1 9 ON While the channel is busy the modem will wait sending only when the channel is clear B1474 BARNETT ENGINEERING LTD PAGE 13 Adjust R12 so that the modem waits when the channel is busy and transmits when the channel is free When the BUSY light is ON the modem is waiting for the channel disable this feature leave P1 9 unconnected and SW1 9 OFF If Option 002 trunking software is used set SW1 9 according to the polarity of the RFCTS signal connected into P1 9 Set SW1 9 and 12 so that the data is only transmitted once the channel has been assigned Send Receive When using the Option 002 trunking software and data buffering use SW1 10 to configure the modexm for send or receive mode Normally all modems within a system should be set for send mode meaning that they will key the trunking radio and wait for RFCTS when data transmission is required Setting SW1 10 ON sets the modem into receive mode In this mode the modem will only hit PTT if the channel has already been established by another modem Having one modem in send mode and
8. Connector Indicators Receive Audio Transmit Audio Squelch Detection PTT 4 Wire Receive 4 Wire Transmit DIP SWITCH SETTINGS Transmitter Level Receiver Level Squelch Polarity Carrier Detect Delay Assert RTS RTS CTS Delay B1474 1200 Baud Bell 202 signaling or V 23 if factory installed 8 data bits no parity 1 stop bit if modem buffering is selected otherwise transparent Operates from 12 to 30 VDC Current drain is 110 mA with the LEDs on 65 mA with the LEDs off 30 C to 50 C Approx 10 x 5 x 1 inside a metal enclosure Compression screw terminals located inside the enclosure RS232 C compatible connections available through a DB 25S socket located on the side of the enclosure Power ON TXD RXD CD RTS CTS BUSY Single ended AC coupled 30 dBm to 0 dBm Single ended AC coupled 20 dBm to 0 dBm Single ended 1M ohm impedance DC coupled detection range 0 to 10 volts polarity is DIP switch selectable Closure to ground for active 0 5 A 50 volts max Balanced 600 ohm impedance 30 dBm to 0 dBm operates full or half duplex Balanced 600 ohm impedance 20 dBm to 0 dBm operates full or half duplex 20 dBm to 0 dBm 30 dBm to 0 dBm Selects high or low going squelch monitor signals 5 or 50 msec Forces RTS on 20 35 50 100 200 300 500 or 1000 msec Allows the transmitter time to reach full power before data is transmitted BARNETT ENGINEERING LTD PA
9. GE 5 PTT Drop Delay Handshaking 2 4 Wire LED Control Equalization Full Half Duplex B1474 0 10 20 50 75 100 or 250 msec Keeps transmitter keyed long enough to ensure squelch tail noise doesn t interfere with data at the receiving terminal Specifies the type of flow control used Selects 2 or 4 wire cable operation Disables LEDs to save power BARNETT ENGINEERING LTD PAGE 6 3 NOTATION Throughout this manual abbreviations will be used These abbreviations are explained here for clarity B1474 CD COS CTS DCE DTE FCC GND PTT RFCTS RTS SOL SW1 8 XOFF XON Carrier Detect Carrier Operated Switch Clear To Send Data Communications Equipment Data Terminal Equipment Federal Communication Commission Ground Push To Talk RF Clear To Send used in trunking systems only Request To Send Squelch This signifies a DIP switch The given example describes the eighth position on DIP switch number one ASCII 13h sent by a receiving station instructing the sending station to halt any transmission ASCII 11h sent by a receiving station instructing the sending station to resume transmission BARNETT ENGINEERING LTD PAGE 7 4 OPERATION The 1474 operates from 12 to 30 VDC to provide an interface between two computer devices and the communications channel In the descriptions below it is assumed that the sending device uses a DCE configuration Four different types of operation m
10. RADIO MODEM B1474 OPERATION MANUAL E BARNETT ENGINEERING April 1998 Manual Revision 4 1 for Version 2 1 Hardware TABLE OF CONTENTS PCC REQUIREMENTS koe 2 2 1 INTRODUCTION oc ty aot wee 3 2 SPECIFIGATIONS dt ne i See Be eel tae es So 5 3 NOTATION esis Sec ca tae eet s ee a a ea 7 4 OPERATIONS tra Weg bo Rods S ugat ub 8 9 SE PUP PROCEDURES isian o Bow st ernie eink 12 6 INDICATORS ke a ee te amp sas 16 7o CONFIGURATION 55 ty Rage 17 8 CONNECTIONS Q aw 19 BOARD ts ca vse at eo ah e P le as ik Y la 20 10 WARRANTY STATEMENT 21 11 APPENDIX A OPERATION WITH TRUNKING SYSTEM 22 B1474 BARNETT ENGINEERING LTD PAGE 1 FCC REQUIREMENTS This equipment generates uses and can radiate radio frequency energy and if not used in accordance with the instruction manual may cause interference to radio communications It has been tested and found to comply with the limits for a Class A computer device pursuant to sub part J of Part 15 of FCC Rules which 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
11. another in receive mode will ensure that both modems do not try to acquire the channel at the same time Set SW1 10 to OFF if using 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 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 single ended input connect P1 5 to ground and use P1 4 to drive the input Receive Gain DIP switch SW2 5 is used to boost the received signal To insert 10 dB of gain turn SW2 5 This will amplify all incoming signals including all valid data tones Equalization Mode 1 To enable the internal amplitude equalizer set SW2 6 ON To leave this feature disabled set SW2 6 OFF Use equalization when there is a large discrepancy in levels between the two tones Carrier Detect Delay Mode 2 When the receiving modem detects carrier it mutes the RXD line for a short time to ensure that transients do not affect the received data Set SW2 7 OFF to delay the received data for 5 msec ON to delay the received data for 50 msec Carrier detect delay should be less than the RTS CTS delay at the sending end Full Half Duplex Mode 3 B1474 BARNETT ENGINEERING LTD PAGE 14 To operate full duplex leave
12. any buffered character restarts modem s drop delay timer e Once the modem stops receiving characters and the PTT drop delay timer expires the mo dem 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 is less than 50 characters B1474 BARNETT ENGINEERING LTD PAGE 25
13. at these connections are made correctly and the proper signals are supplied to each unit order the Option 001 interface cable from Barnett Engineering Ltd Otherwise refer to the manual for the Ericsson GE radio to determine the correct interface points OPERATION The trunking modem operates with some slight timing differences from the conventional modem Hardware Handshaking The sequence followed in obtaining 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 modem The signal is connected to the SQUELCH input on the modem 3 The modem produces tones onto the channel and waits the specified RTS CTS delay This delay is a minimum of 5 msec to ensure that all tones have stabilized before any data is sent 4 When the RTS CTS delay has expired CTS is returned to the sending computer and the transmission of data begins When all of the data has been transferred the sending computer drops its RTS signal causing the modem to drop its CTS signal 5 The modem holds the radio s Push To Talk PTT on the radio until the PTT Drop Delay has expired The channel assignment will not be
14. ay be configured Hardware Handshaking Basic operation and timing using hardware handshaking are as follows e The sending device asserts its RTS and waits e Upon receiving the RTS the associated modem performs the following functions checks the channel if this feature is enabled If the channel is free it asserts its PTT to power up the radio s transmitter presents a mark tone carrier onto the channel sets its RTS CTS delay timer from 20 to 1000 msec RTS CTS delay must be greater than the carrier detect delay at the receiving end e 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 e Data is transmitted any format may be used Once all the data has been transmitted the sending computer drops its RTS e Upon sensing the dropped RTS the sending modem does the following drops CTS immediately its PTT drop delay timer 0 to 250 msec Once the PTT drop delay timer has expired the sending modem releases the radio transmit ter turns off the modem carrier and returns to receive mode For hardware handshaking set XON XOFF signaling off assert RTS continuous off and buffering off Set RTS CTS delay and PTT drop delay as required Refer to Fi
15. by the buyer to Barnett Engineering Ltd Shipment to Barnett Engineering 44 5 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 Barnett Engineering Ltd s liability is specifically limited to its obligation described herein to repair or replace a defective part or parts covered by this warranty 2 Exclusive Warranty The warranty set forth herein is the only warranty oral or written made by Barnett Engineering Ltd and is in lieu of and replaces all other warranties expressed or implied including the warranty of merchantability and the warranty of fitness for particular purpose B1474 BARNETT ENGINEERING LTD PAGE 21 11 APPENDIX OPERATION WITH GE MARC V TRUNKING SYSTEM When ordered with the Option 002 trunking software the B1474 will handle the special timing and control requirements of a GE Marc V trunking system The following sections describe the connections to a trunking radio and the slightly different operation of the radio modem CONNECTIONS The modem connects into the Marc V system the same as it would to a conventional radio as described in section 5 using the PTT RX data and TX data pins The only difference is that the squelch monitor is tied to RFCTS within the radio to determine when the channel is assigned To ensure th
16. e 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 data is sent The delay is active regardless of whether hardware handshaking or data buffering is used PTT A low going push to talk signal is active whenever the modem is transmitting data Squelch Detect If the radio channel is currently being used the modem will not return the CTS signal until the channel is available If XON XOFF signaling is selected XOFF will be returned to indicate a busy channel then XON will be issued when the channel is free This feature may be disabled using a DIP switch PTT Drop Delay This adjustable delay prevents squelch tails from disturbing the received data at the other end of the system Level Selection Transmit levels are adjustable from 0 to 20 dBm The receive section has selectable gain of 10 dB if required to boost low incoming signal levels B1474 BARNETT ENGINEERING LTD PAGE 3 Indicators Modem status condition is indicated by front panel LEDs The LEDs may be disabled to conserve power B1474 BARNETT ENGINEERING LTD PAGE 4 2 SPECIFICATIONS GENERAL Transmission Rate Transmission Format Power Requirement Temperature Range Physical Size Radio and Wireline Data
17. em receives a character from the sending device or transmits any buf fered character it restarts the PTT drop delay timer Once the modem stops receiving characters and the PTT drop 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 RTS CTS delay timer be set to a value less than 500 msec and that the computer respond immediately to an XOFF command B1474 BARNETT ENGINEERING LTD PAGE 24 No Handshaking Basic operation and timing with data buffering no handshaking in a trunking system is as follows The sending computer begins sending data Data format must be 8 bits parity 1 stop bit e Upon receiving data the modem performs the following checks the channel for RFCTS if the channel has been assigned already it asserts its PTT to power up the radio s transmitter If the channel is busy it asserts PTT to ob tain the channel and buffers the received data until the channel becomes assigned presents tones onto the 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 e After the RTS CTS delay timer has expired data is transmitted Receipt of any character or transmission of
18. gure 1 for a summary of the modem timings B1474 BARNETT ENGINEERING LTD PAGE 8 RECEIVE FIGURE 1 MODEM TIMING USING RTS AND CTS B1474 BARNETT ENGINEERING LTD PAGE 9 Software Handshaking Using XON XOFF Basic operation and timing using XON XOFF software handshaking are as follows The sending computer begins sending data The format must be 8 data bits no parity 1 stop bit e Upon detecting data the sending modem performs the following checks the channel if this feature is enabled If the channel is free it asserts its PTT to power up the radio s transmitter If the channel is busy it returns XOFF to the sending computer which halts the transmission of data When the channel becomes free the modem sends XON to the computer which resumes sending data The modem buffers the data while it continues with the following presents mark tone carrier onto the channel sets its RTS CTS delay timer from 20 to 300 msec RTS CTS delay is a misnomer this case as software handshaking does not use RTS and CTS signals It is actually a buffering time between when the modem starts receiving data from the computer and when it starts transmitting This delay must be greater than the carrier detect delay at the receiving end e The modem at the receiving end senses carrier on the line and asserts its CD The received
19. io lines as shown above 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 receive carrier operated switch COS can be monitored to detect when the radio is receiving a signal by connecting the COS line to P1 7 This sig nal is used to inhibit transmissions over a busy channel The input is capable of monitoring a level from 0 to 10 VDC See Squelch Polarity under DIP switch settings to set the COS polarity and level or to disable this feature If using the Option 002 trunking software connect the radio s RFCTS into the squelch input Digital Connection A DB 25S socket on the side of the unit is used to interface with the computer equipment The RS232 interface provides a DCE interface using the following signals B1474 BARNETT ENGINEERING LTD PAGE 12 GND Chassis Pin 1 TXD Pin 2 RXD Pin 3 RTS Pin 4 connect only if using hardware handshaking CTS Pin 5 connect only if using hardware handshaking GND Signal Pin 7 CD Pin 8 The cable and housing on the DB 25S socket must be shielded to conform to FCC part 15 J A standards for emissions Using a non shielded cable may resul
20. lows RTS is always asserted Do not connect the hardware RTS PTT is always asserted i e the radio s carrier is always on There is RTS CTS delay or PTT drop delay e Data generated by the sending device is passed directly through the modem without hand shaking buffering or time delays Data may be any format For no handshaking non buffered operation set XON XOFF signaling off assert RTS continuous on and buffering off Do not connect the hardware RTS and CTS and do not set RTS CTS or PTT drop delays B1474 BARNETT ENGINEERING LTD PAGE 11 5 SETUP PROCEDURES The semiconductors can be damaged by static discharge Proper handling procedures must be followed Do not touch any of the devices inside the modem and work only in a static free clean and dry environment 1 Remove The Top Cover Remove the two center screws on the top cover of the modem to release it from the base Pull straight up on the cover to expose connections and internal DIP switches 2 CONNECTIONS Line Interface Connect the audio wires in accordance with the configurations below 4 wire cable Connect the two transmit wires into pins 4 and 5 of P1 The receive wires con nect into pins 7 and 8 of P1 SW3 3 SW3 4 must be OFF 2 wire cable Connect the two wires into pins 4 and 5 of P1 Ensure that SW3 3 and SW3 4 are ON Radio If the radio is equipped with a 600 ohm balanced interface connect the transmit and receive aud
21. mer from 20 to 300 msec RTS CTS delay is a misnomer in this case as handshaking is not used It is actually a buffering time between when the modem starts receiving data from the computer and when it starts transmitting RTS CTS delay must be greater than the carrier detect delay at the receiving end e 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 Receipt of any character from the sending device or transmission of any buffered character restarts the sending modem s PTT drop delay timer from 0 to 250 msec Once the PTT drop 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 buffered operation set XON XOFF signaling off assert RTS continuous off and buffering on Do not connect the hardware RTS and CTS Set RTS CTS delay and PTT drop delay as required No Handshaking Non Buffered Basic operation and timing with no handshaking no data buffering are as fol
22. t in undesirable radio interference 3 DIP SWITCH SETTINGS The following section describes the function of each DIP switch on the modem The settings are summarized in a table in Section 7 Configuration LED Control The LED indicators may be disabled to conserve power Set SW1 1 OFF to disable the LEDs RTS CTS Delay When the sending device requests transmission a preset delay is inserted before the modem transmits This delay allows the two way radio to warm up or on a cable system allows the tones to settle on the channel before data transmission begins When hardware handshaking is used the modem pauses the sending device by delaying return of the CTS signal When XON OFF or no handshaking are used the 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 from interfering with the data Set DIP switches SW1 5 SW1 6 and SW1 7 for the desired drop delay between 0 and 500 msec as specified in Section 7 Configuration XON XOFF Controls SW1 8 controls whether the modem will send XON and XOFF to the sending computer when the radio channel is busy software handshaking If the
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