ZETRON 748, Technical Manual

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Programming
025-9368H 65
ACCESSING A MODEL 748 BY MODEM
For remote programming, retrieval of billing data, and diagnostics, the Model 748 has an internal
1200/2400 baud modem. It supports auto detection of Bell 212, CCITT V.22 (1200 baud), and
CCITT V.22bis (2400 baud) modulation standards in both answer and originate modes of operation.
The typical method for remote access is to call the Model 748 from the phone side. Once it has
answered the phone line, wait for the overdial prompt and then dial the program access code. This
will set the internal modem of the Model 748 to answer mode, which then responds with a CCITT
V.25 answer sequence. It will then auto detect the calling modem baud rate (1200 or 2400) and
adjust accordingly. When your local modem responds with a “CONNECT” response, press
ENTER
(or RETURN ) and the Main Menu will be displayed.
An alternative method is to use the dial modifier “R” appended to the end of the phone number. This
reverses the operating mode of the calling modem from
Originate to Answer . A number of commas
(“,” = delay characters) are inserted in between the phone number and the “R”. This is to delay the
start of the answer tone until after the Model 748 has answered the phone line and issued its overdial
prompt. When the Model 748 answers the phone line, it gives two seconds of silence (billing delay)
followed by its overdial prompt. It then listens for either Bell answer (2225 Hz), unscrambled marks
at 1200 baud, or overdialed digits. If it hears another modem instead of DTMF tones, the Model 748
will auto detect your modem's baud rate and connect accordingly. When your local modem responds
with a “CONNECT” prompt to your computer screen, press
ENTER and the Model 748 will send the
“ ENTER PASSWORD ===> “ prompt, just as it would to the local RS-232 port.
Once a successful handshake has taken place (i.e. you receive the CONNECT prompt), the Model
748 waits up to 30 seconds for a “Carriage Return” character (what the computer sends when you
press
ENTER
) to be received. If connected in the Answer mode, it has already received the program
access and the Main Menu is displayed. If it connects in the Originate mode, the Model 748 needs
the program access code to validate access to programming.
Once the Model 748 has been accessed by modem, interconnect call are no longer processed (Phone-
to-Mobile, Mobile-to-Phone, ANI-Mobile Repeat) while the phone line is in use. Repeater panel
operation, however, is not affected and can be monitored by the Real Time display function in the
Diagnostic menu.
2100 Hz for 3.3 seconds 2225 Hz Answer tone, or 1200 baud marks
75 millisecond gap
Figure 6. CCITT V.25 Answer Sequence
The Answer sequence is as follows, the 2100 Hz CCITT Answer tone is presented for 3.3 seconds,
followed by a 75 millisecond gap of silence. The actual handshake part of the sequence starts then,
and is composed of a 2225 Hz Answer tone for Bell 212, or 1200 baud unscrambled marks for
CCITT V.22 or V.22bis. The purpose of the 2100 Hz answer tone followed by silence is to disable
echo suppressers in international trunk connections. The answering modem is the one who initiates
the handshake with this sequence.