RAD Data comm operation manual RSD-20/X.21, External Clock for more than one Sub-channel

Page 16

INSTALLATION

RSD-20 OPERATOR'S MANUAL

2.5.1.4 External Clock for more than one Sub-channel

This option enables connection of more than one sub-channel to the line from the P.T.T. service. Generally, the P.T.T. modems supply clock to every line – i.e. the P.T.T. has to provide the clock. Since the modems are all from the same service, the clocks are synchronized. The external buffer will compensate for phase differences between the clocks received from the sub-channels. However, the external buffer option will not compensate for the clock differences, if different clock sources are used.

2.5.2 RSD-20/X.21

The X.21 standard states that DCEs and DTEs will only have one clock signal (signal timing). The direction of this clock is always from the DCE to DTE. This signal timing is used for the transmit clock and receive clock.

According to this standard, four alternatives are available for the synchronization of the system when working with the RSD-20/X.21:

a)Main channel is DTE (attached to a modem).

b)Main and all sub-channels are DCE (attached to DTEs).

c)Main channel is DCE (attached to a DTE and all sub-channels are DTE (attached to modems).

d)Main channel is DCE and sub-channels are mixed (DTEs and DCEs).

2.5.2.1Main channel is DTE (attached to a modem)

In this mode the RSD operates according to the signal timing of clock of the main channel modem. DTEs attached to the RSD-20 sub-channels are synchronized to the mains clock.

DCEs attached to sub-channels are synchronized on their own signal timing. A special buffer, integrated in the RSD-20/X.21, compensates for the phase difference between the modems of the sub-channels and the main channel modem.

2.5.2.2Main and all sub-channels are DCE (attached to DTEs)

In this mode the RSD provides the clock to all ports attached to the main and sub-channels. The RSD’s baud rate should be strapped to the appropriate system baud rate.

2.5.2.3Main channel is DCE (attached to a DTE) and all sub-channels are DTE (attached to modems)

In this mode the RSD’s baud rate is strapped to CLK-1. The DTE attached to the main channel is synchronized to the RSD’s clock, the modems attached to sub-channels 2, 3, 4 should be strapped to external clock, except for the modem attached to sub-channel 1 which should be strapped to internal clock.

NOTE It is also possible to work with the RSD’s internal clock in this mode, but

CLK-1 is preferred.

2.8

Image 16
Contents RSD-20 DUUDQW\ 6DIHW\DUQLQJV HFODUDWLRQRI&RQIRUPLW\ Table of Contents General IntroductionFunctional Description Specifications Indicators PowerOrdering PhysicalInstallation Physical InstallationElectrical Installation AC PowerRear Panel Internal Switches and Strap SelectionRear Panel Installation Installation System Synchronization and Clock Distribution RSD-20/V.35Synchronization on Main Channel Modem Clock Synchronization on Main Channel Modem’s ClockSynchronization on RSD-20 Internal Clock Synchronization on Internal ClockRSD-20 Synchronization on Sub-channelRSD-20/X.21 External Clock for more than one Sub-channelMain channel is DTE attached to a modem Main and all sub-channels are DCE attached to DTEsMain channel is DCE and sub-channels are mixed DTE and DCE Operation Controls and IndicatorsFront Panel Operating Procedure Power Turn OnPower Turn Off OperationFault Isolation Procedure Power SupplyOperational Field Strapping Changes RSD MalfunctionContention SUB-CHANNEL DisableTheory of Operation and Applications IntroductionControl Signals Main Channel Control SignalsSub-channel Control Signals RSD-20/V.35RSD-20/X.21 Theory of Operation and Applications RSD-20 Operators Manual Theory of Operation and Applications Applications RSD-20 Operating ModesTable A.1 X21 Interface Signal Description Appendix aTable B.1 Interface Signal Description Appendix B