ANALOG AND DIGITAL PHYSICAL INTERFACES Habib Youssef, Ph.D youssef@ccse.kfupm.edu.sa Department of Computer Engineering King Fahd University of Petroleum and Minerals Dhahran, Saudi Arabia COMPUTER NETWORK

The RS-232/CCITT V.24 and V.28 Interface Computer Computer Data Data Modem Modem DTE DCE DCE DTE Out of Band Control Out of Band Control DTE : Data Terminal Equipment DCE : Data Circuit Termination Equipment

The RS-232/CCITT V.24 and V.28 Interface (Cont.) Data processing (DTE) to modem (DCE) interface The CCITT V.24 Recommendation defines the interchange circuits V.28 defines the electrical characteristics

The RS-232/CCITT V.24 and V.28 Interface (Cont.) In EIA, known as RS-232-C (the third [-C] version of RS-232) More recent version of RS-232-D (now EIA-232-D) Sometimes TIA-232-D (Telecommunications Industry Association)

The RS-232/CCITT V.24 and V.28 Interface (Cont.) A 25-pin connector/interface ISO 2110 is used Is not part of the RS-232-C standard Bit serial data (full duplex) Out of band control lines

The RS-232/CCITT V.24 and V.28 With Null Modems DTE DCE Null Modem Data Data 2 2 Data Data 3 3 Req to Send Req to Send 4 4 Clear to Send Clear to Send 5 5 Data Set Ready Data Set Ready 6 6 Signal Detect Signal Detect 8 8 Data Terminal Ready Data Terminal Ready 20 20 Signal Ground 7 7 Note : There are many variations to Null Modem Cross Connection

Pin Assignments for V.24/EIA-232 Reserved for testing Secn. CTS Unassigned Shield Clear to Send GND Rx Data Secn. Recv. Line Signal Detector DCE Ready Carrier Detect Tx Data Reg to Send Reserved for testing 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Transmitter signal element timing Secondary RTS Test Mode Transmitter signal element timing Remote Loopback Data Signal Rate Select Transmit signal element timing Local Loopback DTE Ready Secondary received data Ring Indicator Secondary Tx Data

RS-232/CCITT V.24 & V.28 Related Products It is often convenient to switch RS-232/V.24 signals from a computer to one of several devices For example, to different types of printers Simple “multiple” switches are available for this purpose

RS-232/CCITT V.24 & V.28 Related Products (Cont.) Specialized companies have been developed to handle the interface market with products such as Multiple switches RS-232/V.24 cables Null modems RS-232/V.24 “gender changers” Breakout boxes to monitor control signals

Limitations of RS-232/V.28 An upper data rate of about 20 kbit/s An upper cable length of about 50 to 100 feet (about 20 to 40 m) Some products are available to extend these, but a new approach is needed

The Evolution of RS-232-C RS-232-C RS-449 signals RS-422/423 electrical (1977) RS-442 balanced circuits RS-443 unbalanced circuits RS-232-C RS-530 (1987) Balanced Circuits V.35 Balanced Circuits EIA-232-D (1987) Unbalanced circuits

Synchronous Transmission Has a known timing relationship between bits and characters Characters are sent one after the other The receiver recovers this timing from transitions in the arriving data 1 Start End Characters

V.24/EIA-232 dial-up operation

RS-423/CCITT V.10 Single Ended Interchange Circuit Noise Error Recvr Trans Signal return Note: V.10 is the same as X.26 or RS-423-A (unbalanced)

RS-422/CCITT V.11 Differential Interchange Circuit Noise Sensitive to differential signal Recvr Trans Noise was rejected Termination resistor Note : V.11 is the same as X.27 or RS-422-A (balanced)

CCITT X.21 Interface Physical-level interface between DTE and DCE For synchronous operations on public data networks X.21 uses control transitions and ASCII characters rather than using separate signal lines

CCITT X.21 Interface (Cont.) The X.21 electrical characteristics are CCITT X.27 (balanced; same as V.11 and RS-422) CCITT X.26 (unbalanced; V.10 and RS-423) (Note: For operation above 9600 bit/s, X.27 is required) X.21 mechanical characteristics are 15-pin connector per ISO Standard 4903

CCITT X.21 Interface (Cont.) 4 Switched 64 kbit/s X.21 DSU Bridge

CCITT X.21 Interface (Cont.) Circuit Name Direction To DCE / To DTE G Ground,Common Return Ga DTE Common Return X Gb DCE Common Return X T Transmit X R Receive X C Control X I Indication X S Signal Timing X B Byte Timing (Optional) X

CCITT X.21 bis As an interim (perhaps longer term) provision, we have X.21 bis X.21 bis utilizes RS-232 for use with X.25 Particularly used in countries where X.21 has not yet become available

CCITT X.21 bis (Cont.) RS-232 signals are used to represent X.21 events To initiate the call Some X.21 features are not supported Call progress signals

ISDN Interface Terminal Equipment (TE) Network Equipment (NE) Power Source 3 b b c c d d Transmit Transmit Receive e Receive e f f g g Power Source 2 Power Sink2 h h