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2702/03 Auto Call Feature - IBM 2702 Information Manual

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4. The Disable command turns off DTR and RTS.
The Disable command is ended when DTR drops
(turns off). Data Set Ready must turn off within
28 seconds maximum (19.4 seconds minimum)
after DTR and RTS are dropped. No data can
be transmitted or received after the Disable
command has ended.
2702 Data-Set LiD.e Adapter on Private Line
The 2702 data set operation with a private line is
shown in Figure 3-8. The following steps refer to
that figure:
1. The Enable command turns on Data Terminal
Ready (DTR) and Request to Send (RTS).
2. Data Set Ready has to be active (on) for all
read or write operations.
It
is suggested that
this line be turned on when data-set power is
turned on. Data Set Ready has to be active
(on) within
1.
4 ms after DTR and RTS are
turned on. Data Set Ready may be kept on
until the data-set power is turned off, or it
may be turned off after (DTR) and RTS are
turned off.
3. A Write command can start transmitting valid
data within a minimum of one-character-plus-
one-bit time after DTR and RTS are turned on.
If
the communications channel and/or receiving
device cannot handle valid data within that time,
the program must provide the proper delay
either (1) by transmitting pad characters before
the valid data (each pad character provides one-
character-time delay) or (2) by a delay in
issuing the Write command.
4. Data Carrier Detector (DCD) indicates that the
Receive Data lead contains valid data and must
not be turned on until the Receive Data lead
does contain valid data. Data cannot be
received until DCD is active (on). DCD is
ignored during a write operation on a private
full-duplex communications facility. When a
Read is issued, DCD must turn on within one
of the following initial timeout periods:
IBM Terminal Control Type lor II: 3.41 ± 0.110
seconds.
Telegraph Terminal Control Type II: 27.94
±
0.110 seconds.
Data Carrier Detector should turn off within one
character time after the Receive Data lead is invalid.
The Receive Data lead must not go to a space state
for longer than one-character-minus-one-bit time
with DCD on.
5.
If
a terminal drops its RTS lead after sending
an ending character to the 2702 and the Receive
Data lead goes to a space state while carrier
is decaying, the space should start within x-I
bit time (where x is taken from Table 3-1).
The space condition of the Receive Data lead
must not last longer than one-character-plus-
one-bit time.
If
a terminal drops its RTS lead after
receiving an EOT character from the 2702 and
the Receive Data lead goes to a space condition
while carrier is decaying, DCD should drop
within two character times after the first EOT
character was sent.
2702/03 Auto Call Feature
Normal Operation
The 2702/03 Dial command raises Call Request
(CR). The 2702/03 waits for the Auto Call Unit
(ACU) to raise Present Next Digit (PND) as a signal
that the ACU is ready to receive dial digits. Once
PND is up, the 2702/03 places in parallel a four-bit
binary representation of the dial digit on digit leads
NBl, NB2, NB4, and NB8.
(The voltage shift of the
digit leads is negative when they become active).
When the digit lead contains the digit, the 2702/03
raises the Digit Present (DP) line. The ACU should
accept the digit from the four digit lines and then
drop PND while presenting the digit to the dial equip-
ment. Once the ACU drop PND, the 2702/03 will
drop DP but the digit itself will remain on the four
digit lines until the ACU requests the next digit by
raising PND. Raising PND resets the old digit and
signals the 2702/03 to send a new digit.
This operation continues until the last dial digit is
presented to the ACU. After PND and DP drop for the
last dial digit, the digit lines are dropped.
The ACU
will present PND again after having received the last
dial digit, but the 2702/03 will not honor the PND
request and will now wait on Data Carrier Detect
(2702) or Clear to Send (2703 SiS) to end the opera-
tion (normal) or ACR in case of error (no correction
or busy).
Error Operation
Should the phone call not be completed for some rea-
son, some procedure must be provided to terminate
the call. The A CU terminates the call by raising
Abandon Call and Retry (ACR) 7 to 40 seconds after
the 2702/03 raises CR. When the ACU raises ACR,
the 2702/03 resets the four digit lines and then the
CR line. ACR must remain up until CR is dropped.
Once CR drops, the ACU should respond by dropping
Communications Interfaces
3-9

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