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Data Communications
Table 5-5. Modems
DATA RATE
LINE TYPE:
DUPLEX
WIRES
REV.
MODEM
(BITS/SEC)
DIALED/LEASED
FULUHALF
2/4
CHAN.
Asynchronous
Bell103A
300
D/L
H/F
2
No
Bell 202S
1200
D
H
2
Option
Bell202C
ITT GH 2052
Nokia DS 9320
Bell 202T
1200 (3)
L
H/F
2/4
Option
Bell 202D
Vadic VA3400
1200
D
F
2
No
Synchronous (1)
Vadic VA3400
1200
D
F
2
No
Bell 201C
2400
D/L (2)
H/F
2/4
No
Bell 201A
Milgo 2200
Milgo 2400
Bell 208A
4800
L (2)
H/F
4
No
Bell 208B
4800
D
H
2
No
Bell 209A
9600
L (2) (4)
F
4
No
Notes:
1. Synchronous modems require the internal clock modem option.
2. Synchronous operation on a leased line requires the switched carrier modem option.
3. C2 line conditioning allows operation at 1800 bits/sec.
4. Requires D2 line conditioning.
COMMUNICATION PROTOCOLS
Control of computer-terminal communications is required
for the orderly transfer of data. This control is provided in
the form of a protocol or a set of rules and procedures. The
protocol used determines who sends and who receives dur-
ing each phase of communication. In addition the protocol
normally provides for an orderly recovery from communi-
cation errors.
The protocols available with the terminal allow operation
ranging from simple full duplex teleprinter compatibility
to bisynchronous multipoint communications. The various
protocols can be selected by installing the proper interface
and ROM modules. The terminal and the interface can
then be configured to meet your specific requirements.
5-6
The major characteristics of the available protocols are
listed in table 5-6. The following paragraphs discuss each
of these protocols.
CHARACTER PROTOCOLS
Character protocols transmit a single character at a time.
Data checking, if present, is done on individual characters
only (parity). Some configurations allow the transmission
of multicharacter groups but no block checks are made.
There is no automatic retransmission of data following the
detection of 'a data error. Currently available character
mode protocols are Standard, Main Channel, and Reverse
Channel.
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