Programmer 7500

home *** CD-ROM | disk | FTP | other *** search

/ Programmer 7500 / MAX_PROGRAMMERS.iso / PROGRAMS / UTILS / MODEMS / USRMAN.ZIP / SEVEN.ASC < prev next >

Wrap

Text File | 1990-12-27 | 12.6 KB | 550 lines

COURIER HIGH SPEED MODEMS CHAPTER 7. SYNCHRONOUS OPERATIONS OVERVIEW Synchronous mode is required for users who need to call, or receive calls from, a Host computer of a large network. The Host is usually a mainframe. The user's device is often called a terminal, even if it is a powerful personal computer. NOTE: The term DTE in the following discussion means Data Terminal Equipment, the end-to-end equipment involved in data communications. DTE denotes your terminal or computer and the remote computer. Data Rate Synchronization During synchronous operations, transmit and receive clocks at both ends of the phone link control the precise timing of the data flow. The communications equipment at the remote DTE (the modem and network software) and your modem and DTE must all handle the data at the same speed. Protocol Compatibility The devices at both ends of the link must also use the same protocol. These devices are exclusive of the Courier modem, which is transparent during synchronous communications. The Courier's V.42 and MNP error control capabilities are not used. Synchronous Operations 7-1 COURIER HIGH SPEED MODEMS The link protocol may be SDLC (Synchronous Data Link Control), HDLC (High-Level Data Link Control), BISYNC (Binary Synchronous Control) or another protocol determined by the mainframe manufacturer. These protocols format the data into blocks or frames, add control information, and usually provide error control. REQUIREMENTS Courier modems in asynchronous mode adapt to many conditions of remote asynchronous modems. But synchronous connections to a mainframe require strict adherence to specific operating parameters. If you are operating a terminal (not a personal computer) designed for a particular network, you probably need only set the Courier properly before calling or 7-2 Synchronous Operations COURIER HIGH SPEED MODEMS answering. If you have a personal computer, however, you must find out what hardware and software you need before setting the Courier for synchronous calls. What You Need to Know The network's communications management staff can supply information on the following requirements: ∙ The protocol needed for your calls ∙ The software support needed to log into the network, for example, a specific communications package or interface board ∙ The phone number, if you will be calling instead of answering ∙ Whether you need to change the duration of the modem's Request to Send/Clear to Send (RTS/CTS) delay. Once the Courier establishes a synchronous connection, it waits 10 milliseconds (the default value) after receiving an RTS signal from the DTE before responding with a CTS signal. If it's necessary to change the duration of the RTS/CTS delay, you need to reset Register S26. See the S-Register Summary in Appendix B. ∙ Any restrictions about when you can call The RS-232 Interface Transmit and Receive synchronous timing pins are required at the RS-232 interface. You'll need either pin 15 or Synchronous Operations 7-3 COURIER HIGH SPEED MODEMS pin 24 for Transmitter timing signals, depending on whether the modem (pin 15) or the DTE (pin 24) generates the signals. You'll also need pin 17, for Receiver timing signals. If you're using an interface adapter card, described below, the adapter will implement these pins. If you're building your own cable, review the RS- 232 Interface, in Appendix B. The Synchronous Adapter Card As a rule, personal computers do not support synchronous communications. You will probably have to purchase and install 7-4 Synchronous Operations COURIER HIGH SPEED MODEMS a synchronous adapter card. These cards are multifunction boards that provide the following functions: ∙ A synchronous port from the DTE to the modem. ∙ One or more synchronous protocols. Be sure to find out which protocol the Host mainframe requires before you purchase an adapter. ∙ Additional software functions. For example, you need to identify the type of computer or terminal you are using to the mainframe software. You will most likely also have to specify your application, that is, identify the mainframe resources you want to use. SETTING THE MODEM Once the modem is in synchronous mode it no longer recognizes commands. Before attempting to connect in a synchronous network, use the following instructions to configure the modem while it is still in asynchronous mode. NOTE: Be sure that DIP switch 1 is UP (factory setting). The Data Terminal Ready (DTR) override must be OFF so that the Courier detects when the DTE raises and lowers the DTR signal. To set the modem, follow the instructions for issuing commands to the modem that are in Chapter 2, Testing the Installation. Commands begin with a required AT prefix and end with a required Carriage Return, which we denote with the symbol <Enter>. For Synchronous Operations 7-5 COURIER HIGH SPEED MODEMS example, the following command sets the modem to synchronous mode: AT &M1 <Enter> Modulation/Link Rate (Bn, &Nn) Use the following guidelines for your Courier type. V.32 bis modems: If the modem is connecting with another USRobotics V.32 bis modem, set both modems to B0 and to a variable link rate, &N0. The modems will connect at the highest possible rate. If the Courier V.32 bis is to connect with a V.32 modem, set the Courier to B0 and try a variable link rate first, &N0. If that 7-6 Synchronous Operations COURIER HIGH SPEED MODEMS doesn't work, try a fixed link rate of &N6 (9600 bps) or &N3 (2400 bps). HST modems: We do not recommend synchronous communications for these modems because of their asymmetrical modulation, unless you are connecting with another USRobotics HST modem. In that instance, set both modems to B1. For high speed connections with another HST modem, set both modems to a fixed link rate, &N6 (9600 bps) or &N8 (14.4K bps). Find out first, however, if the Mainframe accepts the 14.4K link rate. For 2400-bps connections and lower, set both modems to a variable link rate, &N0. Dual Standard modems: Set the Dual Standard modem to B0. Try a variable link rate setting (&N0) first. If that doesn't work, you may have to set a fixed link rate, for example, &N6 (9600 bps). Flow Control Only the following Courier settings are allowed: &H0 or &H1, &I0, &R0 or &R1. See Chapter 4 for more information on flow control settings. Transmit Clock Source (&Xn) This setting specifies whether the Courier or your DTE generates the Transmit clock timing signals for a synchronous call. Most users will require the default setting, &X0. Synchronous Operations 7-7 COURIER HIGH SPEED MODEMS &X0 The Courier is the source of the Transmit clock timing signals and sends them to your DTE over the RS- 232 interface. Default. &X1 The DTE is the source of the Transmit clock timing signals and sends them to the Courier over the RS-232 interface. This setting is used typically in leased line multiplexed operations. (Multiplexors divide the phone channel so that the channel carries several calls at the same time.) We do not recommend this setting for HST modems. &X2 The Courier's Receiver clock is the source of the timing signals. The signals are looped to the Transmit clock and sent to your DTE over the RS-232 interface. This setting is only used in those systems that require synchronization of 7-8 Synchronous Operations COURIER HIGH SPEED MODEMS data flowing in both directions. We do not recommend this setting for HST modems. Synchronous Mode (&M1) The modem must be set to &M1 for synchronous operation. The modem remains in asynchronous command mode until it makes a synchronous connection with a remote modem. Upon connection, the Courier enters synchronous mode and sends synchronous timing signals to your DTE. Note that the Courier does not respond to commands until it returns to asynchronous Command mode. DIALING OUT Be sure you have set the modem correctly for all of the functions just described under Setting the Modem, including the &M1 setting. The following is a sample command: AT &N6 &M1 <Enter> To call a synchronous Host computer, do the following: 1. Be sure the modem is assembled according to the directions in Chapter 2: a) using the bottom label as a guide, plug one end of the phone cord that came with the modem into the modem jack indicated by the wall jack icon; b) plug the other end of the phone cord into your wall jack; c) plug your phone's cord into the modem's second jack, indicated by the phone icon. Synchronous Operations 7-9 COURIER HIGH SPEED MODEMS 2. Pick up your phone handset and dial the remote system. As soon as you finish dialing, press in the Voice/Data switch. The modem goes off hook in Originate mode and makes the connection. You can hang up your phone. NOTE: If you've changed the setting of the Voice/Data switch, insert S32=1 in the AT . . . &M1 command string described above. This resets the switch's function, so that when you press the switch, the modem goes off hook in Originate mode. ANSWERING You have two options, listed on the next page: Synchronous Answer Mode 1. Before powering on the modem, set DIP switch 5 UP to enable Auto Answer. Then power on the modem and follow the previous instructions under Setting the Modem. OR 2. When the modem is operating with DIP switch 5 DOWN, Auto Answer suppressed, follow the previous instructions under Setting the Modem, but insert S0=1, to enable Auto Answer, in the AT . . . &M1 command string. The modem responds automatically to an incoming call, enters synchronous mode 7-10 Synchronous Operations COURIER HIGH SPEED MODEMS and, if set to &X0, begins sending synchronous timing signals to your DTE. HANGING UP The modem remains online until the remote modem disconnects or your software causes the DTE to drop DTR. The Courier sends the NO CARRIER result code if result codes are enabled, and returns to asynchronous Command mode. Synchronous Operations 7-11