300 BPS Internal Modem (250-1003) Technical Information Faxback Doc. # 4486

MONITOR MODE

After the modem establishes communications with a remote modem, it is
considered to be in the Monitor Mode. While in the Monitor Mode, parameters
are constantly scanned. If any one of these parameters fail, the modem will
break communications and will go Off-Line immediately. The following
parameters are monitored:

CARRIER DETECT

The carrier monitored is that which is sent over the telephone line and to 
the false carrier that may be generated by the modem card. If the carrier
interruption is less than 300 msec., the loss of carrier is ignored.

MANUAL ABORT ENTRY
If you send a CTRL T(14 HEX), or another character that was programmed with
the @ key, and do not send any other character for two seconds, the modem 
card will exit the Monitor Mode. The DTR is also scanned in this mode. If 
the DTR is off, the modem will terminate communications, just as if the 
carrier is ignored.
                                                           
MODEM TRANSMITS A SPACE

If you transmit a long space (a space which is 1.5 seconds or longer), the
Modem will abort communications.

MODEM RECEIVES A SPACE

If the Modem card receives a space from the remote modem that is longer than
three seconds, communications will be aborted.

MODEM HANDSHAKING

END OF DIAL CODE

In the Auto/Originate Mode, after the modem has completed signaling the 
phone line, the Modem will issue a special code through the on-board UART. 
An ACK (06 HEX) is sent just after the modem has finished dialing the tele-
phone number. In applications where the modem is used as a directory dialer, 
not as a communications interface, this code can flag special software. The 
software can then take the Modem On-Hook, so that you may communicate with 
the dialed number using a telephone.

                                                           
COMMUNICATIONS ESTABLISHED CODE

If the Modem receives a valid carrier detect from the telephone lines, it 
will issue a code string to the computer. When the computer receives a line 
feed, carriage return (0A 0A 0D HEX), the communications channel is ready. 
The three byte code sequences will operate at any time (in all modes of 
operation) the modem receives true carrier over the telephone lines.

COMMUNICATIONS FAILED CODE

A code sequence is sent when the modem fails to establish communications, or
when it escapes the Monitor Mode to the Off-Line Mode. This sequence is:

  NAK, line feed, carriage return (15 0A 0D HEX).

This sequence is valid in all operating modes.

AUTO ORIGINATE WITH "NO NUMBER TO DIAL" DETECT

If you have failed to program at least one valid character into the Dialer
memory, the modem will abort the On-Line mode two seconds after the X com-
mand is issued. If there is a character or space programmed into the dialer 
memory by accident, the modem will assume that is the number and proceed to 
dial (if the character can be dialed). The Modem will then wait for 25.6 
seconds before aborting the unsuccessful dial attempt.

COMMUNICATIONS EXAMPLES

The following illustrates some of the methods you can use while in either 
the Manual or Automatic and/or the Originate or Answer modes.

1. With the Tandy 1000 and the communications software initialized, to use 
   the default parameter settings, type: *X. When the *X command is used, 
   the modem will look for the carrier detect. If a number has not been 
   dialed, the modem will hang up after not locating a true carrier.
   The Manual/Originate mode is useful when receiving computer files (such 
   as programs) from a remote computer using communications software.

2. At power-up, in order to change parameters to Auto Dial so that the 
   telephone number 1234567 will automatically be dialed, press L for the 
   List command. Then type the following:

  *MD1234567X
                                                           
3. With the system fully initialized, to indicate Fast Tone dialing of the
   above telephone number, you would type:

   *MFDT1234567X

4. To change the modem setting to Answer, after disconnect type:

   *AX

5. To change to Originate Mode, and dial the telephone number as indicated 
   in #4 above, type:

   *(to turn off WAITING FOR RING)
   *OX

6. After disconnect from #5, go to Manual Answer by typing:

   *MAX

7. After disconnect from #6, go to Manual Originate by typing:

   *OX
                                                           
8. After disconnect from #7, go to Auto Answer by typing:

   *MAX

(abo-07/28/93)