Equinox Systems MEGAPORT, Справочник по аппаратуре

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38 Equinox MEGAPORT Hardware Reference Manual
Special Considerations
When connecting devices to the MEGAPORT board ports, it is
important to understand the difference between DCE and DTE
devices. This is to ensure that data flows in the right direction. If
DCE and DTE are not wired correctly, communications between the
two devices may be blocked.
DCE - Data Communications Equipment such as modems.
DTE - Data Terminal Equipment such as terminals and
printers.
It is also important to understand the difference in terminology
between DB-25 and modular wired installations.
Wiring Conventions
In general, with conventional wiring, DTE devices can only be
connected to DCE devices. This ensures, for example, that the
output of the terminal is routed to the input of the modem. For
example, computer terminals (DTE devices) should be connected to
DCE ports, such as the 990117 DB-25 distribution panel and the
210036 modular adaptor.
This is performed (1) in DB-25 environments with conventional,
straight through cables, and, (2) in the modular environment with
single reversing modular cables and one modular adaptor.
Non-Conventional Wiring
In some situations, it may be necessary to do a non-conventional
interconnection. It is possible to connect DTE devices to other DTE
devices and DCE devices to other DCE devices. For example, if two
terminals or ports must be placed back-to-back without intervening
modems.
This is done in DB-25 environments with null modem cables.