The Resource Magazine For Apple, Atari, and Commodore ...

3O COMPUTEI September/October, 198O. Issue 6
RECEIVER SIGNAL ELEMENTTIMINGPIN 17:
Signals on this circuit are used to provide the
terminal with received signal element timing infor
mation. The transition from ON to OFF condition
shall normally indicate the center of each signal
element "Received Data." Timing information on
"Receiver Signal Element Timing" shall be provided
at all times when circuit "Received Line Signal
Detector," is in the ON condition. It may, but
need not, be present following the ON to OFF
transition of "Received Line Signal Detector."
UNASSIGNED PIN 18: This pin may be used by
the manufacturer for any purpose desired.
SECONDARY REQUEST TO SEND PIN 19:
This signal is equivalent to "Request To Send"
except that it requests the establishment of the
secondary channel instead of requesting the establish
ment of the primary data channel.
Where the secondary channel is used as a back
ward channel, the ON condition of "Request To
Send" will disable "Secondary Request To Send"
and it will not be possible to condition the
secondary channel transmitting data set to transmit
during any time interval when the primary channel
transmitting data set is so conditioned. Where
system considerations dictate that one or the
other of the two channels be in transmit mode at
all times but never simultaneously, this can be
accomplished by permanently applying an ON condi
tion to "Secondary Request To Send" and controlling
both the primary and secondary channels, in
complementary fashion, by means of "Request To
Send." Alternatively, in this case, "Secondary
Clear To Send" need not be implemented in the
interface.
When the secondary channel is useable only for
circuit assurance or to interrupt the flow of
data in the primary data channel, "Secondary
Request To Send1' will serve to turn ON the
secondary channel carrier. The OFF condition of
"Secondary Request To Send" will turn OFF the
secondary channel carrier and thereby signal an in
terrupt condition at the remote end of the communica
tion channel.
DATA TERMINAL READY PIN 20: This signal
is used to control switching of the data set to the
communication channel. The ON condition prepares
the data set to be connected to the communication
channel.
SIGNAL QUALITY DETECTOR PIN 21: Signals
on this circuit are used to indicate whether or noi
there is a high probability of an error in the received
data.
As ON condition is maintained whenever there
is no reason to believe that an error has occurred.
An OFF condition indicates that there is a high
probability of an error. It may, in some
instances, be used to call automatically for the
retransmission of the previously transmitted data
signal. Preferably the response of this circuit shall
be such as to permit identification of individual
questionable signal elements on "Received
Data."
RING INDICATOR (CE) PIN 22: The ON condi
tion of this signal indicates that a ringing signal
is being received on the communication channel.
DATA SIGNAL RATE SELECTOR PIN 23:
Signals on this circuit are used to select between
the two data signaling rates in the case of dual
rate synchronous data sets or the two ranges of
data signaling rates in the case of dual range
non-synchronous data sets.
An ON condition shall select the higher data
signaling rate or range of rates.
The rate of timing signals, if included in the
interface, shall be controlled by this circuit as may
be
appropriate.
TRANSMIT SIGNAL ELEMENT PIN 24: Signals
on this circuit are used to provide the transmitting
data set with signal element timing information.
The ON to OFF transition shall nominally indi
cate the center ol each signal element on "Trans
mitted Data." When "Transmit Signal Element
Timing" is implemented in the data set, the data
set shall normally provide timing information on
"Transmit Signal Element Timing" whenever the
data set is in a power on condition. It is permissible
for the data set to withhold timing information on
this signal for short periods provided "Request To
S e n d '' i s i n t h e O F F c o n d i t i o n .
UNASSIGNED PIN 25: This pin may be used by
the manufacturer for any purpose desired.
Although the "EIA" publishes an interface standard,
some data set manufacturers do not conform to the
standard in all cases. CHECK the specifications on
each data set to determine which signals are on each
pin. ©
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