2.5.3.3 1200 Baud DDD Circuit 



The second class of circuit (1200 baud dialup) has the following 

 characteristics : 



Channel Type 



Modulation Rate 



Coding 



Error Control 



Block Length 



Block Check 

 Character 



DDD subscriber lines; half-duplex, AT&T 

 type 202C modem or equivalent 



1200 baud (120 characters/s) 



asynchronous ASCII (10 bits) even parity 



block transmission: ACK/NAK 



320 (max) data characters, and 6 framing 

 characters with 6 device control characters 



Longitudinal Redundancy Check (LRC) 



NOTE: CDF assumes user terminal on 1200 baud circuits to have the 

 characteristics of a Texas Instruments Model 742, with options: 



(1) "Auto-answer" line discipline. 



(2) "Answer-back qpemory" preprogramed with user ID. 



(3) Bell 202C data set compatible modem. 



The TI Model 742 can transmit and receive at 120 characters per 

 second (CPS), but its printer operates only up to 30 CPS. The CDF 

 uses control character sequences to remotely command the terminal 

 recorder and printer. Table 3 lists the possible commands. The 

 platform sensor data are disseminated at 120 characters per second 

 rate with the terminal's printer OFF. An end-of-line (carriage 

 return, line feed) is inserted following every 80 data characters 

 by the CDF. 



TABLE 1 



TI 742 COMMAND CHARACTERS 



Command 



Record ON 



Playback OFF 



Printer ON 



Printer OFF 



Auto Device Control ON (ADC ON) 



Auto Device Control OFF (ADC OFF) 



(*) Utilized by DPS/DCS. 



Code 



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