V.24
The Recommendation V.24 of the ITU-T is intended primarily to an interface for data transmission to standardize. For this purpose, it describes interface lines and their function in a data transmission system between a data terminal device ( DEE , DTE ) and a data transmission device ( DÜE , DCE ).
This recommendation has been adapted several times to the technical conditions. Of the more than 50 originally described functions, 37 have been used since 2000.
The DIN standard DIN 66020-1 corresponds to V.24 from 1996. The American standard RS-232 also describes interface cables .
Device manufacturers are generally free to use these interface cables, but are recommended by ITU-T for certain analog modem types .
Applications
By combining the different interface lines, different data transmission variants can be implemented:
- Serial asynchronous communication (computer / PC technology)
- Serial synchronous communication (professional technology, e.g. the German Datex-P network)
- Data transmission via an additional auxiliary channel (Backward channel / Secondary channel); z. BV23 modems when BTX is introduced
- Parallel communication (V.19; V.20 is out of date)
development
Interface cables with the designation 1xx (102, 103 .., 100 series) are intended for DEE-DÜE communication (modem functions).
The functions of the 200 series, which were removed in 2000, were designed for connection establishment in dial-up networks. The associated procedure ( V.25 ) for transferring the dialing characters to a dialable device still exists, but only for the direction to the transmission network. The interface control of the DEE via the V.24, lines of the 200 series has been removed.
The following ITU-T recommendations V.25bis, V.250 (formerly V.25ter) use lines from the 100 series to establish connections.
An optional device for establishing a connection is referred to as an automatic dialing device for data connections (AWD). It is an external device or integrated in a modem.
Described interface lines
Although the international standards are partially similar, the naming is very different:
- ITU numbers the interfaces from 100 or from 200.
- DIN assigns letters with consecutive digits due to the function:
- E = earth or ground line
- D = data line
- S = control line
- M = message line
- T = clock line
- P = test lead
- PS = test control
- PM = test message
- H = auxiliary channel
- HD = auxiliary channel data
- HS = auxiliary channel control
- HM = auxiliary channel message
- W = select bit
- RS-232 uses a name similar to DIN, but only with letters:
- A = earth or ground line
- B = data line
- C = control or reporting line
- D = clock line
- S = auxiliary channel
The abbreviations in the first column of the table are used colloquially. The pin number refers to the D-Sub -25 design.
| ITU | DIN | RS-232 | Pin code | Description according to DIN 66020-1 | Description according to ITU-T V.24 / RS-232 | |
|---|---|---|---|---|---|---|
| Earth lines (return lines, earth connections) | ||||||
| GND | 102 | E2 | FROM | 7th | Plant earth | Signal ground or common return / signal ground |
| 102a | E2a | DEE return conductor | DTE common return | |||
| 102b | E2b | DÜE return conductor | DCE common return | |||
| 102c | E2c | Return line for single-current interfaces | Common return | |||
| Data interfaces | ||||||
| TXD, TX, TD | 103 | D1 | BA | 2 | Transmission data | Transmitted data see Note 1 |
| RXD, RX, RD | 104 | D2 | BB | 3 | Receive data | Received data s. Note 1 |
| Interfaces for controlling a data transmission | ||||||
| 108/1 | S1.1 | 20th | Switch on the transmission line | Connect data set to line s. Note 2 | ||
| DTR | 108/2 | S1.2 | CD | DEE ready for operation | Data terminal ready s. Note 2 | |
| RTS | 105 | S2 | CA | 4th | Switch on the transmitter | Request to send s. Note 3 |
| 124 | S3 | Use all frequency groups | Select frequency groups | |||
| SEL | 111 | S4 | CH | 23 | Switch on high transmission speed | Data signaling rate selector (DTE source) s. Note 4 |
| 126 | S5 | 11 | Switch on the high transmission frequency | Select transmit frequency | ||
| 127 | S6 | Switch on the low receiving frequency | Select receive frequency | |||
| RFR | 133 | S7 | CJ | 4th | Retrieve received data | Ready for receiving s. Note 3 |
| 116/1 | S8.1 | Switch on substitute operation | Back-up switching in direct mode | |||
| 116/2 | S8.2 | Prepare replacement operation | Back-up switching in authorized mode | |||
| 130 | S9 | Send confirmation tone | Transmit backward tone | |||
| 136 | S10 | Short post-effect time | New signal | |||
| 129 | S11 | Switch on the receiver | Request to receive | |||
| 132 | S12 | Replace data operation | Return to non-data mode | |||
| Interfaces for controlling an auxiliary channel (backward or secondary channel) | ||||||
| SXMT | 118 | HD1 | SBA | 14th | Auxiliary channel send data | Transmitted backward channel data |
| SRCV | 119 | HD2 | SBB | 16 | Auxiliary channel receive data | Received backward channel data |
| SRTS | 120 | HS2 | SCA | 19th | Switch on auxiliary channel transmitter | Transmit backward channel line signal / secondary request to send |
| SCTS | 121 | HM2 | SCB | 13 | Auxiliary channel ready to send | Backward channel ready / secondary clear to send |
| SDCD | 122 | HM5 | SCF | 12 | Auxiliary channel received signal detection | Backward channel received line signal detector |
| 123 | HM6 | Auxiliary channel reception quality | Backward channel signal quality detector | |||
| Clock lines for synchronous data transmission | ||||||
| TCK | 113 | T1 | THERE | 24 | Sending step rate to the DCE | Transmitter signal element timing (DTE source) |
| XCK | 114 | T2 | DB | 15th | Signal element send clock from the DCE | Transmitter signal element timing (DCE source) |
| 128 | T3 | Receive step act to the DCE | Receiver signal element timing (DTE source) | |||
| RCK | 115 | T4 | DD | 17th | Signal element reception clock | Receiver signal element timing (DCE source) |
| 131 | T5 | Receiving-side scanning mark | Received character timing | |||
| Control lines for test conditions | ||||||
| 140 | PS2 | 21st | Switch on remote test loop / test mode | Loopback / maintenance test | ||
| 141 | PS3 | 18th | Switch on near test loop | Local loopback | ||
| Message lines for data transmission | ||||||
| DSR | 107 | M1 | CC | 6th | Operational readiness | Data set ready |
| CTS | 106 | M2 | CB | 5 | Readiness to send | Ready for sending / Clear To send |
| RNG, RI | 125 | M3 | CE | 22nd | Incoming call | Calling indicator / ring indicator |
| 112 | M4 | CI | 12 | High transmission speed | Data signaling rate selector (DCE source) s. Note 3 | |
| DCD, CD | 109 | M5 | CF | 8th | Received signal detection | Data channel received line signal detector / (Data) Carrier detect |
| SQD | 110 | M6 | CG | 21st | Reception quality | Data signal quality detector |
| 134 | M7 | Receive data identification | Received data present | |||
| 117 | M8 | Replacement operation | Standby indicator | |||
| Message line via test status | ||||||
| 142 | PM1 | 25th | Test condition | Test indicator | ||
| Analog interfaces for voice response | ||||||
| 191 | A1 | Sent voice response | Transmitted voice answer | |||
| 192 | A2 | Voice response received | Received voice answer | |||
| Interfaces of the 200 series for controlling an AWD according to ITU V.25 or DIN 66021-4 (separate plug connection) | ||||||
| 201 | E22 | 7th | Plant earth | Signal ground or common return | ||
| 206 | W21 | 14th | Select bit 1 | Digit signal (2 0 ) | ||
| 207 | W22 | 15th | Select bit 2 | Digit signal (2 1 ) | ||
| 208 | W23 | 16 | Select bit 3 | Digit signal (2 2 ) | ||
| 209 | W24 | 17th | Select bit 4 | Digit signal (2 3 ) | ||
| 202 | S21 | 4th | Occupy the transmission line | Call request | ||
| 211 | S22 | 2 | Accept dialing characters | Digit present | ||
| 203 | M21 | 22nd | Transmission line busy | Data line occupied | ||
| 210 | M22 | 5 | Readiness to accept dialing characters | Present next digit | ||
| 205 | M23 | 3 | Choice unsuccessful | Abandon call | ||
| 204 | M24 | 13 | Called station switched on | Distant station connected | ||
| 213 | M25 | 6th | Operational readiness | Power indication | ||
Note 1: This only applies to serial data transmission. Parallel modems according to V.19 have a different assignment.
Note 2: There are two ways to start a data transfer:
- 108/1: By activating this interface, the transmission device immediately seizes the line; the presence of an opposing device is not checked. This option is therefore only useful for dedicated connections.
- 108/2: The DTE is ready for operation, the transmission device is waiting to be activated. An incoming call, manual pressing of the user's data key or the M24 interface line of an AWD switches the transmission device to the line.
Note 3: The double pin assignment of RTS and RFR often leads to confusion in data flow control . This is described in ITU-T recommendation V.43.
Note 4: RS-232 puts the lines CH and CI on the same pin 23; they cannot be used at the same time.
Measuring devices at interfaces
Interface tester 100 series
Interface tester 200 series
Additional international standards from ITU and ISO
- Mechanical description of frequently used connections:
- ISO 2110 (25-pin), used for common analog modems; often called “ Cannon plug ” in laboratory slang .
- ISO 4902 (37-pin), used with modems according to V.36
- ISO 4903 (15-pin), use in synchronous data networks according to X.21
- ISO 2593 (34-pin), used with modems according to V.35 , often also referred to as MRAC connector
With analog modems (also in PC technology, ⇒ COM interface) levels according to V.28 are usually used.
- Data transfer formats:
- V.4
swell
- ITU-T V.24 (03/93 and 02/2000)
- DIN 66020-1 (July 1999)
- The pin assignment comes, among other things, from devices of the Deutsche Bundespost .
literature
- Joe Campbell: V 24 / RS-232 communication , Sybex-Verlag, 1984, ISBN 3887450752