Data button

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The data key (also known as modem key ) in a telephone is used to connect a modem to the telephone line. Telephones equipped with this have been around since at least 1966; At the time, they could only be rented from what was then the Deutsche Bundespost . Today the data key is no longer important , in April 1996 Deutsche Telekom discontinued the service for one of the last types of these telephones, the FeTAp 756 D.

FeTAp 756 D with data key (left) and earth key

history

technology

Until about 1988 post-approved modems were not dial-up and did not have a built-in data button. A remote data connection could then be started in three ways:

• The most common type of connection was via telephones with a data button. To transfer data, a connection to the communication partner is first established manually via the telephone. If the modem on the other side is in automatic mode, it immediately connects to the line and sends out a signal tone of 2100 Hz. During this tone, the caller must press the data key on their own telephone, the modem then takes over the connection. If automatic mode is not activated, the remote station accepts the telephone connection and will also start the manual connection via the data key.
• An automatic connection establishment via an external automatic dialing device for data connections (AWD) according to ITU-T recommendation V.25 with interface lines of V.24 . A few types of modems had an internal add-on board with this function. An AWD functionally simulates a telephone with a data button.
• The modem starts the data transfer automatically when you receive a call. This function can be switched off manually; it is also described in V.25.

ADo 8

Originally, all of the telephones mentioned here were equipped with junction box technology. When establishing a connection, the potential of the a-wire is placed on connection point G (external charge indicator ) by removing the handset . By pressing the data button, the b-wire is connected to connection W (external alarm clock ). The circuit for data key recognition within a modem (often a relay , more rarely an optocoupler ) was located between connections G and W.

TAE

Due to the introduction of the new TAE connection technology around 1990, the existing telephones with data buttons had to be converted, there was no new development afterwards (the FeTAp 616 D could not be converted and was taken out of service). By pressing the data key, the potential of the b-wire is switched to connection point G. At the same time, the speech circuit within the telephone is short-circuited in order to suppress disturbing noises. The connection point G is now called W and is the contact point 3 of a TAE socket.

costs

Telephones with data buttons could only be rented from the Deutsche Bundespost until 1990. Excerpts from the first historical price list after the liberalization of the terminal equipment market:

• The standard telephone with a rotary dial cost 2.39 DM per month (comparative price).
• A telephone with a data key was charged at 8.21 DM; it was absolutely necessary for the operation of a modem.
• AED: The monthly rent was DM 49.59.
• An AWD in 1990 cost a monthly rent of DM 40.01; an additional 14.99 DM was added for maintenance. This connection option was not very common.

Naming

The designation of the telephones with a data key follows the nomenclature of the Deutsche Bundespost at the time: the first two digits for the device type, the third digit is 6 (equipment variants). Instead of a flag , however, the data key was installed on the left and a D added after the telephone name.

There are the following types: FeTAp 616 D, FeTAp 716 D, FeTAp 736 D, FeTAp 756 D and FeTAp 796 D. The FeTAp 616 D has the standard color pebble gray.

The interrogation devices for data terminal equipment (AED 77 and AED 83) were special devices with which up to 20 individual telephones with data buttons could be replaced. At the request of the participant, an AED was used for more than 5 connection lines.

Individual evidence

1. ^ Central Telecommunications Office, Section B 34, slide archive. Row 64.01, image 18, data transmission, DK 621.391, 9.1969, photo of the standard postmodem D 1200 S with FeTAp 616 D, description on the slides: DBP, FTZ / FSA Dmst, Urh: FTZ VIII B / 1966
2. ^ Letter from the central telecommunications office to distributor T 32/1 dated July 6, 1989, conversion instructions for telephones with data keys
3. ↑ FTZ letter, see above
4. ↑ FTZ letter, see above
5. ↑ Official Journal of the Federal Minister for Post and Telecommunications and the German Federal Post Office, No. 59, year 1990, June 29, 1990, price list for the rental and maintenance of telecommunications terminals that were previously made available according to the conditions of use under public law
6. ↑ Picture of a FeTAps 616 D
7. ↑ Image of a FeTAps 716 D ( memento of the original from June 14, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  
8. ↑ Further information on AED 77 ( Memento of the original from March 4, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.