RADIO MODEM B1474 OPERATION MANUAL April, 1998 Manual Revision 4.1 (for Version 2.
TABLE OF CONTENTS FCC REQUIREMENTS . . . . . . . . . . . . . . . . . . . 2 1 INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . 3 2 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . 5 3 NOTATION . . . . . . . . . . . . . . . . . . . . . . . . 7 4 OPERATION . . . . . . . . . . . . . . . . . . . . . . . . 8 5 SETUP PROCEDURES . . . . . . . . . . . . . . . . . . . 12 6 INDICATORS . . . . . . . . . . . . . . . . . . . . . . . 16 7 CONFIGURATION . . . . . . . . . . . . . . . . . . . .
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.
1 INTRODUCTION The B1474 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.
Indicators Modem status condition is indicated by front panel LEDs. The LEDs may be disabled to conserve power. B1474 BARNETT ENGINEERING LTD.
2 SPECIFICATIONS GENERAL Transmission Rate: 1200 Baud (Bell 202 signaling) or V.23 if factory installed Transmission Format: 8 data bits, no parity, 1 stop bit if modem buffering is selected; otherwise transparent Power Requirement: Operates from 12 to 30 VDC. Current drain is 110 mA with the LEDs on, 65 mA with the LEDs off. Temperature Range: -30oC to +50oC Physical Size: Approx.
PTT Drop Delay: 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. 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.
3 NOTATION Throughout this manual, abbreviations will be used. These abbreviations are explained here for clarity. B1474 CD Carrier Detect COS Carrier Operated Switch CTS Clear To Send DCE Data Communications Equipment DTE Data Terminal Equipment FCC Federal Communication 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.
4 OPERATION The B1474 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 may be configured: Hardware Handshaking Basic operation and timing using hardware handshaking are as follows: • The sending device asserts its RTS and waits.
FIGURE 1 B1474 MODEM TIMING USING RTS AND CTS BARNETT ENGINEERING LTD.
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. • 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.
– 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 timer (from 20 to 300 msec). RTS/CTS delay is a misnomer in this case as handshaking is not used.
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.
GND (Chassis) TXD RXD RTS CTS GND (Signal) CD Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 7 Pin 8 (connect only if using hardware handshaking) (connect only if using hardware handshaking) 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 result in undesirable radio interference. (3) DIP SWITCH SETTINGS The following section describes the function of each DIP switch on the modem.
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. To 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 R12 so that the data is only transmitted once the channel has been assigned.
To operate full duplex, leave SW2.8 OFF. To operate half duplex, set switch SW2.8 ON. If a 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.
6 INDICATORS 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 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.
7 CONFIGURATION SWITCH 1 SWITCH 2 LED CONTROL TX LEVEL (INTO 600 OHMS) 1 X 1 LEDS OFF LEDS ON 3 4 X X X X X X X X X X X X 3 Radio (dBm) -4 -6 -8 -10 -12 -14 -20 -24 X RTS/CTS DELAY 2 2 X msec 20 35 50 100 200 300 500 1000 X X X X X X X X X X Bal0 -2 -4 -6 -8 -10 -16 -20 RX GAIN 5 X dB 0 10 PTT DROP DELAY 5 6 7 X X X X X X X X X MODE 1 (EQUALIZATION) msec 0 10 20 50 75 100 250 6 X NO RECEIVE EQUALIZATION RECEIVE EQUALIZATION MODE 2 (CD DELAY) 7 XON/XOFF X CD DELAY =
SWITCH 3 RTS ON 1 X EXTERNAL RTS RTS ON AT ALL TIMES BUFFER 2 X USE RTS/CTS CONTROL USE BUFFER RTS ON 3 4 X X B1474 4 WIRE CABLE 2 WIRE CABLE BARNETT ENGINEERING LTD.
8 CONNECTIONS P1 AUDIO PIN SYMBOL DESCRIPTION 1 +V INPUT VOLTAGE 2 GND GROUND 3 TX RADIO TRANSMIT OUTPUT, SINGLE ENDED 4 TX WL 5 TX WL 6 RX RADIO 7 RX WL 8 RX WL 9 SQL SQUELCH DETECTOR INPUT 10 PTT PUSH TO TALK OUTPUT P3 } TRANSMIT OUTPUT, BALANCED RECEIVE INPUT, SINGLE ENDED } RECEIVE INPUT, BALANCED 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
9 BOARD LAYOUT B1474 BARNETT ENGINEERING LTD.
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.
11 APPENDIX A - OPERATION WITH A 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.
FIGURE 2 MODEM TIMING FOR A GE MARC V TRUNKING SYSTEM USING RTS/CTS HANDSHAKING B1474 BARNETT ENGINEERING LTD.
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. • Upon detecting data, the sending modem performs the following: – checks the channel. If RFCTS has already been assigned (the channel is available), it asserts its PTT to power up the radio’s transmitter.
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, no parity, 1 stop bit. • 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.
