P_ED1000

ED1000

ED1000 is a technique to connect a teletype to a central office with 2 wires. A Frequency Shift Keying (FSK) modulation is used to send and receive simultaniously. It is like a MODEM (V.21) but with different carrier frequencies.

SEU-A/B Standard

Definitions / Naming

Type	Definition
A	Central Office, Switching Exchange, EDS, (PC Sound Card)
B	Terminal Station, Teletype

Type 'B' is the normal configuration for a teletype. Some teletypes can be configured as type 'A' to be connected directly to another teletype.

Levels and Frequencies

SEU	Direction	Frq A (space, 0)	Frq Z (mark, 1)	Level	U rms *	U peak *
A	Send	500Hz	700Hz	-14.5dBm	0.146V	0.206V
A	Receive	2250Hz	3150Hz	≥-34.0dBm	≥0.015V	≥0.022V
B	Send	2250Hz	3150Hz	-9.0dBm	0.275V	0.389V
B	Receive	500Hz	700Hz	≥-28.5dBm	≥0.029V	≥0.041V

*: at termination of 600Ohm

Seeing the lower frequencies as a bit value '0' and the higher as '1', the bit values can be used as from a TTL async. serial adapter.

Max. Line Length

Distance	Conductor Diameter
20km	0.8mm
14km	0.6mm
10km	0.4mm

Max. Line Loss

Direction	Frequency Band	Loss
A → B	600Hz ± 100Hz	14dB
B → A	2700Hz ± 450Hz	25dB

---

ADo8 Plug

It is common for ED1000 system to use an ADo8 plug.

Pin	Description
1	Line a
2	nc
3	nc
4	Line b
5	Bridge to 6
6	Bridge to 5
7	nc / Paper-End-Switch
8	nc / Paper-End-Switch

The line wires are used to send and receive at the same time like a MODEM on phone wires.

The bridge between pin 5 and 6 is for signaling a connected plug. May be high voltages can be used by teletype to detect the bridge!

Some teletypes use a switch (relay) on pin 7 and 8 to signal paper end.

---

Protocol

Legend:

Symbol	Description
AT	User presses the button 'AT' (German: 'Anruf-Taste') on the teletype to start a call
ST	User presses the button 'ST' (German: 'Schluß-Taste') on the teletype to end a call
✠	User presses the key '✠' (WRU, German: 'Wer da?') to retrieve the ID from the other teletype
✦	User presses the button '✦' on the teletype or on a ✠-request the teletype sends automatically its ID
T	User presses any key on the keyboard to type the message
WB	If the central office is ready-for-dialing (after pressing button 'AT'), it signals this state. Here it is shown with symbol 'WB' (German: 'Wahlbereitschaft')
A	If the connection to an other teletype is established, the central office signal the teletype to switch on the power of the teletype/printer
Z	If the connection to an other teletype stopped, the central office signal the teletype to switch off the power of the teletype/printer

Note: In software the symbols 'WB', 'A' and 'Z' are used as escape sequences to trigger the state.

Outgoing Call

TODO

Idle mode ...

Begin a Call and Dialing

Pressing button AT on FSG...

Connecting

On fail...

On success...

Transmitting Content

The user can now press keys on the keyboard to type the message. The characters are send as they are typed a maximum speed of 6.6 characters per second (400 per minute).

If using a punch tape for sending (or typing fast enough) the characters are transmitted without a pause with maximum speed.

---

Ending a Call

Pressing button ST...

Ending by other side...

---

Incoming Call

---

✠ WRU (Wer da?)

Note: 'WRU' is the english short form of 'Who are You'

On an established connection every side can send the '✠' character and the other machine responds automatically with its ID in text form. The ID is coded in Baudot-Murray-Code.

The user can press the button '✦' to send the ID of his own machine.