CHAPTER THREE
3.12 RS-232 TIME WORD OUTPUT (TALKER)
3.12.1 INTRODUCTION
This output is designed in accordance with EIA RS-232C/RS-422 specification and is used to
provide an electrical interface between any TM7000 timing instrument and the RS-232/RS-422
serial interface. This section provides the user with configuration information.
3.12.2 GENERAL DESCRIPTION
This talker output can be divided into two sections: Time extraction and RS-232/RS-422
communication. The RS-232/RS-422 communication portion will be the main focus of this
section. The time extraction portion of this output is invisible to the user. The time is updated
every millisecond unless the unit is sending a time message. It is suggested that the user read
this section in its entirety for a better understanding of the options provided and what they mean.
3.12.3 TERMINAL TYPE
There are two basic configurations that need to be described before serial communication can be
discussed: Data Communication Equipment (DCE) and Data Terminal Equipment (DTE). The
major differences between the two configurations are their rules and pin assignments. DTE is
designated as the initiator of the commands. DCE is designated as the responder to the
commands. This terminal (talker) is configured as DCE. It is important to remember that
most computer RS-232 communication ports are set up in the DTE configuration, which dictates
that this unit be configured as DCE.
3.12.4 DCE HANDSHAKING
This talker is expecting at least two signals from the user’s equipment: DTR and RTS. A third
possibility would be TXD and it would only be used in the asynchronous mode. When the DTR
signal is not active, the DSR and CTS signals will both be inactive and this unit will not send any
time messages. When the DTR signal goes active, the DSR and CTS signals will both go active.
A time message will be transmitted only when both DTR and RTS are both active. If RTS goes
inactive while a time message output is in progress, the time message output will be paused until
RTS returns to active, at which time the time message will resume. A partial message can be
cleared by setting DTR inactive.
3-42 TM7000 TymMachine TCG/T (Rev D) Symmetricom, Inc.
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