1200 BPS DCM-212 Modem (260-1385A) Speed Options Faxback Doc. # 7056
The DCM-212 Modem automatically synchronizes with standard speed rates of
300 and 1200 bits per second (bps).
Switching from high speed (1200 bps) to low speed (300 bps) operation
occurs when the DCM-212 receives either the wake-up code in the Tandy
protocol mode or the Attention code in the Hayes protocol mode. When the
modem detects 1200 bps after receiving the code sequence, it communicates
in high speed. If the modem is awakened at 300 bps, it uses low speed
operation.
The originating station always determines the speed of operation. If you
wake up the DCM-212 in low speed mode but intend to call a high speed modem,
the DCM-212 will select the low speed 300 bps operation if the remote modem
has low-speed detection circuitry. If you intend to call a high-speed modem,
you must set the DCM-212 to high speed before calling a remote modem.
COMMUNICATIONS PROTOCOL
Certain criteria must be met before computer-to-computer communication can
occur. The modem operates on 10 or 11-bit data words. The following
combinations are allowed:
START BIT DATA BIT PARITY BIT STOP BIT
COUNT COUNT COUNT COUNT
1 8 NO 1
1 8 NO 2
1 7 YES 1
1 7 YES 2
1 7 NO 2
The condition of 1 start bit, 7 data bits, no parity bit and only 1 stop
bit will be auto recognized as having a marking or spacing 8th data bit. A
communication error could result if you do not use at least 10 bits as
shown above. If you must operate with fewer than 10 bits, remember that
abort sequences, where character recognition is needed, might not operate.
Long space disconnect and carrier drops will, however, still operate.
When opened for programming by the wake-up or attention code sequence, the
DCM-212 automatically synchronizes the speed rate, word length, parity, and
stop-bit numbers (communications protocol) of your computer system.
NOTE: One modem must be in originate mode and the other must be in answer
mode. usually, when you call another computer, you should be in originate
mode. When you receive a call, you should be in answer mode.
MANUAL V. AUTOMATIC OPERATION
When you want to dial an information service (such as CompuServe or Dow
Jones News Service) or communicate with another person whose computer is
also using VIDTEX, set the modem to manual operation mode. In this mode,
you can control what the system does by manually dialing and answering the
phone.
When you want the DCM-212 to dial a phone number or answer the phone for
you, set it to automatic operation mode. In this mode, the modem dials the
phone number you store in its memory or answers the phone when someone calls
you. Automatic mode, for instance, lets you dial the information service
number without picking up the phone--just type the number along with the
proper DCM-212 programming commands on the computer keyboard.
ORIGINATE V. ANSWER MODE
To place a call to an information service or another person using VIDTEX,
set the DCM-212 to originate mode. In this mode, the call originates from
your computer. When you want to receive a call (answer the phone), set the
DCM-212 to answer mode. Note that originate and answer modes can be used
either manually or automatically.
HELPFUL TIP:
When you use your DCM-212 for the first time or when you seem to be getting
garbled data, use the self-test mode to help you find the cause of thee
problem. Refer to the section on "self-test" in Appendix A, TANDY PROTOCOL
REFERENCE, or in Appendix B, HAYES PROTOCOL REFERENCE.
If you plan to use the DCM-212 in Tandy protocol mode only, you can skip
Chapter 3 and Appendix B. Or, if you intend to use your modem in Hayes mode
only, you can disregard Chapter 2 and Appendix A. For further operation
information, refer to the operation manual that accompanies your
communications software package.
(dkh-08/05/093)