The Leader in Industrial Data Communication Solutions

1. The Leader in Industrial Data Communication Solutions Training: Serial Elements

2. Section:Getting Started

3. Data-Linc Group • Industrial grade products include: • Wireless Modems • Ethernet Radio Modems • Serial Radio Modems • Copper Wire Modems • Dial-up/Leased Line • Dedicated Wire FSK Modems • Specialty: • Analog/Discrete Multiplexers • 4-Port Switch • Accessory Devices • Factory pre-configured for your application

4. Modem? • Modulator – Demodulator • Used for short and long distance data communications

5. Duplex? • Simplex • One way communication only • Full Duplex • Simultaneous two-way communication • Half Duplex • Two way communication but one direction at any instant in time

6. Modem Block Diagram

7. Section:User Equipment Interface

8. User Equipment Interface • Electrical Standards Supported: • RS232 • DLG can provide cables/pinouts for most applications • Others developed with your assistance (no charge) • RS485 (optional) • RS422 (optional) • Data-Linc RS485 and RS422 Options • RS485 is always two wire • RS422 is always four wire • Some applications require + and – polarity reversal

9. RS232 DTE and DCE • DTE: Data Terminal (PC) Equipment • DCE: Data Communications (Modem) Equipment • DTE to DCE cabling is straight through wiring

10. RS232 DTE Connectors (PC) • Viewed looking into the connector

11. RS232 DCE Connectors (modems) • Viewed looking into the connector

12. RS232 Voltage Levels • Voltages of -3v to -25v with respect to signal ground (DB9 pin 5, db25 pin 7) are considered logic '1' ( mark condition), whereas voltages of +3v to +25v are considered logic '0' (space condition). The range of voltages between -3v and +3v is considered a transition region for which a signal state is not assigned.

13. RS232 Pin Functions • Clear to Send (CTS). This signal is asserted (logic '0', positive voltage) by the DCE device to inform the DTE device that transmission may begin. RTS and CTS are commonly used as handshaking signals to moderate the flow of data into the DCE device. • DCE Ready (DSR). When originating from a modem, this signal is asserted (logic '0', positive voltage) when the following three conditions are all satisfied: • 1 - The modem is connected to an active telephone line that is "off-hook";2 - The modem is in data mode, not voice or dialing mode; and3 - The modem has completed dialing or call setup functions and is generating an answer tone. • Ground. All signals are referenced to a common ground, as defined by the voltage on this pin. This conductor may or may not be connected to protective ground inside the DCE device. • Received Data (RxD). This signal is active when the device receives data. When no data is transmitted, the signal is held in the mark condition (logic '1', negative voltage). • Request to Send (RTS). This signal is asserted (logic '0', positive voltage) to prepare the DCE device for accepting transmitted data from the DTE device. Such preparation might include enabling the receive circuits, or setting up the channel direction in half-duplex applications. When the DCE is ready, it may acknowledge by asserting Clear to Send. • Received Line Signal Detector (CD) (also called carrier detect). This signal is relevant when the DCE device is a modem. It is asserted (logic '0', positive voltage) by the modem when the telephone line is "off-hook", a connection has been established, and an answer tone is being received from the remote modem. The signal is deasserted when no answer tone is being received, or when the answer tone is of inadequate quality to meet the local modem's requirements (perhaps due to a noisy channel). • Transmitted Data (TxD). This signal is active when data is transmitted. When no data is transmitted, the signal is held in the mark condition (logic '1', negative voltage).

14. Info: Synchronous / Asynchronous • Serialized data is not generally sent at a uniform rate through a channel. Instead, there is usually a burst of regularly spaced binary data bits followed by a pause, after which the data flow resumes. Packets of binary data are sent in this manner, possibly with variable-length pauses between packets, until the message has been fully transmitted. In order for the receiving end to know the proper moment to read individual binary bits from the channel, it must know exactly when a packet begins and how much time elapses between bits. When this timing information is known, the receiver is said to be synchronized with the transmitter, and accurate data transfer becomes possible. Failure to remain synchronized throughout a transmission will cause data to be corrupted or lost.Two basic techniques are employed to ensure correct synchronization. In synchronous systems, separate channels are used to transmit data and timing information. The timing channel transmits clock pulses to the receiver. Upon receipt of a clock pulse, the receiver reads the data channel and latches the bit value found on the channel at that moment. The data channel is not read again until the next clock pulse arrives. Because the transmitter originates both the data and the timing pulses, the receiver will read the data channel only when told to do so by the transmitter (via the clock pulse), and synchronization is guaranteed. Techniques exist to merge the timing signal with the data so that only a single channel is required. This is especially useful when synchronous transmissions are to be sent through a modem. Two methods in which a data signal is self-timed are nonreturn-to-zero and biphase Manchester coding. These both refer to methods for encoding a data stream into an electrical waveform for transmission.In asynchronous systems, a separate timing channel is not used. The transmitter and receiver must be preset in advance to an agreed-upon baud rate. A very accurate local oscillator within the receiver will then generate an internal clock signal that is equal to the transmitter's within a fraction of a percent. For the most common serial protocol, data is sent in small packets of 10 or 11 bits, eight of which constitute message information. When the channel is idle, the signal voltage corresponds to a continuous logic '1'. A data packet always begins with a logic '0' (the start bit) to signal the receiver that a transmission is starting. The start bit triggers an internal timer in the receiver that generates the needed clock pulses. Following the start bit, a fixed number of bits of message data are sent bit by bit at the agreed upon baud rate. The packet is concluded with an optional parity bit and mandatory stop bit.

15. Asynchronous Data Framing • Data-Linc products may support 10 and/or 11 bit words. Refer to product specification sheets • Bit count is calculated by adding the number bits composing the word • Bit count = start + data bits + parity + stop bits

16. Carrier Control • Two Methods of Carrier Control: • RTS (RS232 pin – Hardware Control) • This method places modem Tx/Rx control responsibility onto the user attached equipment. Some equipment does not provide this capability. • DSCC (Data Sense Carrier Control) • Embedded in the modem’s control logic. • Operates by monitoring received data from the user attached equipment and controls carrier automatically. • The Data-Linc LLM1100 includes DSCC.

17. Carrier Control (Cont.) RTS high turns the transmitter on. When low the receiver is on.