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C O N N E C T O R S
The following paragraphs describe the external connectors and their
f u n c t i o n s .
R C I C O N N E C T O R ( J 4 )
T h e S T U - I I I / E i n t e r f a c e s t o t h e E x t e r n a l R e m o t e C o n t r o l l e r ( E R C )
via aserial input/output port called the Remote Control Interface
(RCI) located on the rear panel of the STU-III/R (see Figure 3-2).
The RCI connection is made via a25-pin female D-type connector
with apinout as shown in Table 3-2. The RCI provides four distinct
functions: remote control, analog voice, push-to-talk, and LPC input
e n a b l e . E a c h o f t h e s e f u n c t i o n s a r e d e s c r i b e d i n d e t a i l b e l o w .
R e m o t e
C o n t r o l
The remote control function provides full external control of the
STU-III/R by the ERC. It permits activation of functions normally
considered operator functions for the desktop STU-III. All STU-
III/R configuration and control is directed over the RCI. The remote
control interface is an asynchronous RS-423A electrical interface
that uses RS-232C protocol and operates at 9600 bps. The STU-III/R
functions as aData Communication Equipment (DCE), and the ERC
as aData Terminal Equipment (DTE).
A n a l o g Vo i c e
Analog voice is passed to the ERC over afour-wire interface
physically located on the RCI port. This four wire audio interface
consists of a600 ohm balanced receive and transmit pair. Technical
specifications for this interface are provided in Table 3-3.
P u s h - t o - Ta l k ( P T T )
The STU-III/R can be configured for either Voice Activated Switch
(VOX) or Push-To-Talk (PTT) operation. When configured for push-
to-talk, the PTT connection on the RCI is used to control half-duplex
voice transmissions in secure mode. Each time PTT is asserted, the
STU-III/R will initiate ahalf-duplex voice transmission if it is not
currently receiving. The PTT signal is active low (logic 0=
asserted), and will remain nonasserted if unused.
3 - 3
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