General Product Description
The model SLR-96 and SLQ-96 radio modems provide a reliable high-speed data link between computers or data terminals operating at data rates from 1200 to 9600 bps. Though both models are functionally equivalent, the SLR-96 is housed in an attractive desktop enclosure and includes a 120/240 VAC power supply (with connections for an external backup battery) and an optional duplexer, while the SLQ-96 features a utility enclosure, operates on +12.5 VDC, and the duplexer must be mounted externally. Both models have separate radio transmitter and receiver modules mounted internally.
Radio data transfer. Because the modems use radio rather than wirelines to transfer data, they must be used in pairs or as part of a multiunit system, and the operating radio frequencies of the units must match in order to communicate properly. An operating license issued by the Federal Communications Commission (FCC) also must be obtained before the units can be placed in service.
The modem is designed to transfer data transparently; i.e., the data applied to the transmitting modem is output by the receiving modem without alteration. No data error correction schemes-which would typically add overhead data and thus slow the data transfer speed-are provided by the modem; all information processing (i.e., addressing, CRC, forward error correction, etc.) is performed by the data terminal equipment (DTE), not the modem.
Reliability. The modem transfers data just as reliably as typical wireline modems (the rated bit error rate is 1 ¥ 105 at an RF signal strength of 90 dBm). The receiving modem automatically drops the squelch tail from any incoming data signal, preventing data errors that are commonly associated with squelch noise. Also incorporated in the design is a data scrambler, which provides the necessary data transitions if a continuous string of ones or zeros must be transmitted. To prevent system lockup, a watchdog timer monitors the operation of the modem every 1.4 seconds and automatically resets it if a failure occurs.
Point-to-point or multipoint. The modem is ideal for either point-to-point or multipoint applications. Point-to-point operation simply transfers data between locations; multipoint systems typically use high-speed polling schemes controlled by a central unit to selectively send and receive data to and from other modems in the system. Because the SLR/SLQ is a transparent modem, the data terminal equipment (DTE) connected to each modem must supply the polling intelligence in a polled system.
Half or full duplex. The SLR-96 and the SLQ-96 can be ordered from the factory in either a half- or a full-duplex configuration. Half duplex means that the modem can transmit and receive data, but it cannot transmit and receive at the same time. Full duplex, on the other hand, means that the modem can transmit and receive data at the same time. Full-duplex operation typically requires two assigned radio operating frequencies and a duplexer, a passive radio device that allows simultaneous transmission and reception of radio signals through the same antenna.
Compatibility. Interface to the modem from the customer-supplied DTE is RS-232 (RS-422/RS-485 optional) via a DB-25 connector. To the DTE connected to the unit, the modem looks like a typical wireline modem. Character length can be set to 6, 7, or 8 bits with even, odd, or no parity. The modem can be configured (using a DIP switch) to communicate with the DTE synchronously or asynchronously, with internal or external transmit clocking in the synchronous mode.
The modem's transmitter can be set to operate in a switched mode (where the DTE controls transmitter keying) or in a continuous mode (where the transmitter is always keyed and is not controlled by the DTE).
The modem allows selection of either a full hardware handshaking mode (where data transfer between the DTE and modem is controlled by handshake signals [DTR and CTS for transmit, DCD and DTR for receive] between the two pieces of equipment) or a three-wire mode (where the modem ignores handshaking signals and begins processing data from the DTE whenever it detects the first data character from the DTE).
The modem contains a 2K buffer (1K transmit data, 1K receive data) that is used during data transfer to buffer the data and provide the necessary transmit and receive time delays (a delay of approximately 9 milliseconds is required to stabilize the transmitter before data can actually be transmitted).
We recommend anti-glare glasses when working with the SLR/SLQ.
Mechanical & Electrical Specifications
The SLQ-96 features a rugged iridited aluminum RFI enclosure that can be used in a variety of operating environments. Because of the modem's relatively compact design, the duplexer, if required, must be mounted externally. All status indicator lights are mounted internally and can be seen only when the cover is removed.
Power Requirements. The SLQ-96 operates from a +12.5 VDC source (negative ground) and has built-in reverse polarity protection. No overvoltage protection is provided, however, so care should be used in selecting and hooking up a power source. The current drain when the modem is transmitting is 1.5 amps maximum; in the receive/standby mode, it is 0.5 amp maximum.
Mounting Requirements. Figure 1 shows the mechanical mounting dimensions for the SLQ-96, including the four mounting holes located on the base plate.
Connectors and Controls. Figure 2 identifies the connectors and controls located on the end panel of the SLQ-96 and also provides Repco part numbers for the appropriate mating connectors needed for the external connections.
The SLR-96 modem is housed in an attractive all-metal enclosure that is suitable for desktop use in an office environment. The unit measures 2.2 in. ¥ 10.0 in. ¥ 11.7 in. and includes sufficient space for an internally mounted duplexer.
Power Requirements. The SLR-96 operates on 120 or 240 VAC but also has a connection for an external, user-supplied 12.5 VDC backup power source. The current drain with the backup source connected is 1.5 amps maximum when the unit is transmitting and 0.5 amp maximum in the receive mode. Reverse polarity protection is built in; no overvoltage protection is provided, however, so care should be used in selecting and hooking up a power source.
Connectors and Controls. Figure 3 shows the connectors and controls located on the rear panel of the SLR-96. Repco part numbers for the appropriate mating connectors are also shown.
*mates with type N male coaxial connector.
Input/output signal connections for the SLR-96 and SLQ-96 are made via a standard DB-25 (25-pin D) connector (both models have the same pin functions). The pinouts for the DB-25 are shown in Figure 4 and listed in Table 1; all signals meet standard EIA RS-232 specifications. Additional descriptions of each I/O signal and its function are provided following Table 1.
|1||1 Chassis ground|
|2||TXD (transmit data)||To modem|
|3||RXD (receive data)||From modem|
|4||RTS (request to send)**||To modem|
|5||CTS (clear to send)||From modem|
|6||DSR (data set ready)||From modem|
|8||DCD (data carrier detect)||From modem|
|15||Internal Tx clock*||From modem|
|17||Receive clock*||From modem|
|20||DTR (data terminal ready)**||To modem|
|24||External Tx clock*||To modem|
*Used only for synchronous operation.
**Handshaking signals that must be supplied by the DTE to operate in the full hardware handshaking mode (if DTR is not available from the DTE, DTR can be strapped to DSR to provide proper handshaking).
TXD (transmit data). Data sent from the DTE to the modem for transmission to a remote modem.
RXD (receive data). Data that has been received by the modem from a remote location and is subsequently being transferred back to the data terminal equipment from the modem.
RTS (request to send). Active only when operating in the full hardware handshaking mode (and not in the three-wire mode), RTS is a handshake signal from the DTE to the modem that informs the modem that the DTE needs to transmit data. The modem responds by keying the transmitter-if it is not already keyed as it would be in the continuous mode-and, after a timed delay of between 0200 ms (switch-selectable at the modem), sending a CTS signal to the DTE.
CTS (clear to send). A handshake signal active only in the full hardware handshaking mode (and not in the three-wire mode), CTS is sent from the modem to the DTE to inform the DTE that the modem is ready to transmit data. CTS must always be preceded by an RTS signal from the DTE to the modem. The delay between RTS and CTS can be set between 0200 mS at the modem.
DSR (data set ready). DSR is supplied by the modem to the DTE whenever the modem is turned on and ready to receive data from the DTE.
DCD (data carrier detect). DCD is a handshaking signal that is active in the full hardware handshaking mode but not in the three-wire mode. The modem sends a DCD signal to the DTE whenever the modem receives an on-frequency transmission from another modem. The DTE responds with a DTR signal if it is ready to receive data.
Internal Tx Clock (synchronous operation only). When operating synchronously, the modem provides an internal clock signal to control the transmission of data to the DTE. (An external transmit clock signal from the DTE can be substituted if applied at pin 24).
Receive Clock (synchronous operation only). The modem provides a receive clock signal at pin 17 for synchronous clocking of data transferred between the modem and the DTE.
DTR (data terminal ready). DTR-another handshaking signal that is active in the full hardware handshaking mode but not in the three-wire mode-is sent from the DTE to the modem in response to a DCD signal from the modem. DTR indicates that the DTE is ready to receive data from the modem.
NOTE: If the DTE is not set up to supply a DTR signal to the modem, the DTR line can be strapped to the DSR line at the modem connector to provide proper handshaking.
External Tx Clock (synchronous operation only). If the modem's own internal transmit clock is not used to provide transmit clocking, a transmit clock signal from the DTE can be substituted if applied on pin 24.
Status lights, which monitor the status of the input/output lines, are located on the front panel of the SLR-96 (see Figure 5) and inside the case on the SLQ-96. A jumper (JS-17) on the processor board can be used to enable or disable the bank of lights as desired. Brief descriptions of the function of each status light follow Figure 5.
DSR (data set ready). The modem is ready to transmit or receive data.
DTR (data terminal ready). The data terminal is ready to receive data from the modem.
RTS (request to send). A signal to the modem that the data terminal has data to transmit.
CTS (clear to send). A signal to the data terminal that the modem is ready to receive data.
TXD (transmitting data). The transmitter is keyed and the modem is transmitting data.
RXD (receiving data). The modem is receiving valid data from another modem.
DCD (data carrier detect). The modem is receiving a radio signal that is the proper frequency but may or may not carry valid data.
TX (transmit). The modem's transmitter is keyed.
RX (receive). The modem's receiver is on.
TM (test mode). The modem is operating in the test mode (the test mode is selected using jumper JS-10 on the modem's processor board).
DIP Switch Settings
Three banks of DIP switches (a total of 24 switches) located on the processor board are used to configure a wide range of operating parameters. Table 2 lists the switches and their functions and is followed by brief descriptions of all of the switch settings. Most units are configured at the factory according to customer specifications and generally do not require changes in the DIP switch settings before being placed into service. Whenever a DIP switch setting is changed, the SLR/SLQ must be restarted for the change to take effect.
Note that functions such as I/O data rate, three-wire time-out, CTS delay, and character length are determined by groups of switches rather than a single switch setting. For specific switch settings for these functions, refer to the individual switch descriptions.
|SW1-1 to SW1-8||Not used|
|SW2-1||I/O data rate (to/from the DTE) (see table 3)|
|SW2-2||I/O data rate (to/from the DTE) (see table 3)|
|SW2-4||Three-wire time-out (see table 4)|
|SW2-5||Three-wire time-out (see table 4)|
|SW2-6||CTS delay (see table 5)|
|SW2-7||CTS delay (see table 5)|
|SW2-8||CTS delay (see table 5)|
|SW3-1||Half duplex (open), full duplex (closed)|
|SW3-2||Tx mode: switched (open), continuous (closed)|
|SW3-3||Rx mode: switched (open), continuous (closed)|
|SW3-4||Stop bits: one (open), two (closed)|
|SW3-5||Character length (see table 6)|
|SW3-6||Character length (see table 6)|
|SW3-7||Asynchronous (open), synchronous (closed)|
|SW3-8||9600 bps (open), 4800 bps (closed) select*|
* Selects the rate of RF data transfer between SLR-96 modems, not the I/O data rate between the SLR-96 and the DTE (see SW2-1.-2)
I/O Data Rate (SW2-1, -2). The I/O data rate (the rate of data transfer between the SLR-96 and the DTE, not to be confused with the RF radio-to-radio data rate selected by SW3-8) can be set to 1200, 2400, 4800, or 9600 bps, according to the switch settings in Table 3. If 9600 bps is selected, then SW3-8 must also be set to 9600 bps.
Three-Wire Time-out (SW2-4, -5). In the three-wire mode the modem ignores all handshaking signals to and from the DTE and keys the transmitter when the first data character from the DTE is detected (just as if the RTS line was set true). To accommodate the delay required to stabilize the transmitter before transmitting data (approximately 9 milliseconds), the modem momentarily buffers the data from the DTE.
The three-wire time-out duration (the delay between when the modem detects the last bit of data from the DTE and when it stops transmitting) is selected according to Table 4.
NOTE: If the three-wire mode is disabled, the modem operates using full hardware handshaking.
|O||O||three-wire mode disabled|
|C||O||5 millisecond time-out|
|O||C||100 millisecond time-out|
|C||C||500 millisecond time-out|
CTS Delay (SW2-6, -7, -8). After receiving an RTS signal from the DTE, the modem waits a predetermined amount of time-the CTS delay-before sending a CTS signal back to the DTE. The length of the CTS delay is selected according to the switch positions shown in Table 5.
|O||O||O||0 millisecond delay|
|C||O||O||5 millisecond delay|
|O||C||O||10 millisecond delay|
|C||C||O||25 millisecond delay|
|O||O||C||50 millisecond delay|
|C||O||C||100 millisecond delay|
|O||C||C||150 millisecond delay|
|C||C||C||200 millisecond delay|
Half Duplex/ Full Duplex (SW3-1). Half-duplex operation (switch open) means that the modem cannot transmit and receive data at the same time, while full-duplex operation (switch closed) means that the modem can transmit and receive data simultaneously.
Tx Mode (SW3-2). When configured to the switched mode (switch open), the modem keys and then unkeys the radio transmitter whenever a data transmission is made. In the continuous mode (switch closed) the transmitter is keyed continuously-something that is usually done only with full-duplex modems.
Rx Mode (SW3-3). The Rx mode typically corresponds to the Tx-mode setting of the companion modem (the remote modem that the local modem is talking to). When the remote modem's transmitter is set to switched, the local modem's Rx mode should also be set to switched (this tells the local receiver to expect interruptions in the received signal and not to interpret these interruptions as data errors). On the other hand, if the remote modem's transmitter is set to continuous, the local modem will expect to continually receive an RF signal and should, therefore, also be set to continuous.
Stop Bits (SW3-4). A stop-bits setting determines whether one or two bits are transmitted after each character to indicate the character's end. Most systems require one stop bit (switch open), although some require two (switch closed).
Character Length (SW3-5, -6). Character length of data words can be set to 6, 7, or 8 bits with even, odd, or no parity. The appropriate character length is determined by the data format used by the DTE connected to the modem and is selected using the switch settings shown in Table 6.
|C||O||8 bits (8 + none; 7 + parity)|
|O||C||7 bits (7 + none; 6 + parity)|
|C||C||6 bits (6 + none; 5 + parity)|
Asynchronous/Synchronous (SW3-7). Asynchronous or synchronous operation is selected according to the data-transfer format used to communicate with the DTE.
Asynchronous data transfer consists of a start bit and a stop bit at the beginning and end, respectively, of each data byte. These start and stop bits control data flow and eliminate the need for precise synchronization of the communicating data devices. Asynchronous operation is typical for most personal computers.
Synchronous data transfer-typically much faster than the asynchronous mode-relies on the synchronization of the transmitting and receiving devices, in this case the modem and the DTE. Precise timing devices in both units (transmit clocking can be supplied by either the modem or the DTE) are used to maintain synchronization. Synchronous transmission is often typical for terminals operating in a mainframe environment.
RF Data Transfer Rate (SW3-8). The rate of RF data transfer between radio modems can be set to either 9600 bps (switch open) or 4800 bps (switch closed). This setting should not be confused with the I/O data rate, which is the rate of data transfer between the radio modem and the DTE and is controlled by switches SW2-1 and -2. However, if the I/O data rate is set to 9600 bps, then the RF data transfer rate (SW3-8) also must be set for 9600 bps.
A number of modem operating parameters are determined by jumpers that are located on the processor p.c. board and the interface p.c. board. These jumpers allow the modem to accommodate interconnection with a variety of DTEs.
The status of each of the jumpers is determined by a header assembly, which slides down over the pins and can easily be repositioned. All jumper positions (left/front, right/back) are referenced with the modem's cover removed and the front panel (with its row of LEDs) facing forward.
Processor Board Jumpers
Table 7 shows all of the jumpers that are located on the modem's processor p.c. board (jumpers on the interface board are listed in Table 8) and is followed by a brief description of each jumper's function.
RTS (JS-2). As shown in Figure 6, JS-2 determines whether the processor reads the signal from the DTE that is on the RS-232 RTS line (the normal mode) or reads the line as always being true (the forced mode).
The RTS light on the front panel shows the state that the processor is reading, not the state of the RTS line (in the forced mode the RTS light will always be illuminated).
DSR (JS-6). The position of JS-6 (refer to Figure 7) determines if the DTR line is looped back and used to provide the DSR signal to the DTE (the normal mode) or if the DSR line is forced true (the forced mode). Before reaching the RS-232 DSR line, however, the DSR signal is further qualified by the test mode signal, which, if present, will not allow the DSR line to be true.
The DSR light on the front panel always indicates the state of the DSR line.
DTR (JS-7). The DTR line status read by the processor is determined by the position of jumper JS-7 (see Figure 7). In the normal mode, the processor reads the status of the DTR line coming in from the DTE. In the forced mode, JS-7 is set so that the processor will always read the DTR line as true.
The DTR light on the front panel shows the DTR state that the processor is reading, not the state of the actual RS-232 DTR line (in the Forced mode the DTR light is always illuminated).
CTS (JS-8). JS-8 (see Figure 8) determines whether the RS-232 CTS signal sent to the DTE is generated by the processor (the forced mode) or forced true at all times by the jumper (the normal mode).
The CTS light on the modem's front panel shows the state of the line coming from the processor, not the actual state of the RS-232 CTS line (in the forced mode, even though the RS-232 line is forced true, the CTS light continues to monitor the CTS signal coming from the processor.
TEST (JS-10). The test jumper is read by the processor at power up, and if the jumper is in the testing position, the modem places itself in the test mode.
WATCHDOG (JS-11). The watchdog timer prevents system lockup by monitoring processor activity. When the watchdog timer is enabled, the processor must access the timer at least once every 1.4 seconds or the modem is automatically reset to its start-up state.
LEDs (JS-17). The position of JS-17 determines whether the status indicator LEDs are enabled or turned off. This feature is typically used primarily in model SLQ-96 modems where the LEDs are located inside the housing.
Modem Interface Board Jumpers
In addition to the seven jumpers located on the processor board and described in the preceding section, two jumpers are also located on the modem interface board (see Table 8).
|Jumper||Description||Pin 1 to 2||Pin 2 to 3|
SCRAMBLE (JS-1). The position of JS-1 determines if the data sent between modems is scrambled. The modem is normally set to operate in the scrambled mode in order to provide a constant transmitted spectrum density and thus eliminate discrete line components that might cause interference. The scrambler also insures that a minimum density of clock transitions will be present for proper operation of the clock recovery circuit. The scrambler can be disabled for testing purposes.
RX DATA (JS-2). JS-2 tells the modem circuitry within the SLR/SLQ that it will be receiving inverted or noninverted data from the radio receiver. Typically, this jumper will remain in the inverted position and will not have to be changed by the user.