Dynapro Technologies Dynapro ET TCS, Руководство разработчика приложений, Страница: 22 / 337

2-8
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Request to Send (CA) (Output)
In the TCS, Request to Send (RTS) is always on immediately after the power-up sequence
and self-tests have finished executing. RTS remains on except during a reset, a long break, or
if the power to the TCS is switched off.
NOTE
This use of Request to Send complies with the RS-232-E standard but precludes operating the TCS in
half-duplex mode.
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Clear to Send (CB) (Input)
The TCS polls Clear to Send (CTS) each time a code is to be transmitted to the DCE over the
serial link. If CTS is off, the code is not sent. When the DCE switches CTS off, transmission
from the TCS halts on the next code boundary. The TCS can be set up to ignore this signal in
3-wire systems.
Normally, the standard does not allow the DCE to switch CTS high or low at random.
However, this technique is commonly used to allow DCE to halt transmission from the TCS
via a hardware signal. Allowing switched operation of CTS to halt transmission is
compatible with operation as described by the RS-449 standard.
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Data Set Ready (CC) (Input)
Data Set Ready (DSR) is set on by the DCE when ready for operation. The TCS polls DSR
before every code transmission to the DCE. If DSR is off, the code is not sent to the DCE.
The TCS can be set up to ignore this signal in 3-wire systems.
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Data Terminal Ready (CD) (Output)
Data Terminal Ready (DTR) is switched on by the TCS as soon as the power-up sequence
and self-tests are concluded. DTR remains on at all times, except during a reset or long
break. DTR is switched off for the duration of the reset or long break signal and is reasserted
on following the break, regardless of the state of the DSR.
The RS-232-E standard specifies that once DTR is switched off by the terminal, DTR can not
be driven on again until Data Set Ready from the DCE is switched off. Because the TCS
supports a minimal 3-wire, RS-232-E interface where unconnected control circuits such as
DSR are biased on, DTR operation is independent of DSR.
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Data Carrier Detect (CF) (Input)
Data Carrier Detect (DCD) is switched on by the DCE whenever the DCE detects a suitable
primary carrier in the receive state. The primary carrier is the telephone line connection, or if
a null-modem cable is used, the proper hard-wired connection. RLSD allows one station to
determine whether the station at the other end has valid contact. If RLSD is off, the Received
Data line is ignored by the TCS.
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Secondary Request to Send (SCA) (Output)
Secondary Request to Send (SRTS) is switched off by the TCS whenever the TCS stalls the
host. SRTS is switched on by the TCS whenever the TCS unstalls the host. The SRTS line
can be used to implement a control line hold-off of the host.