Intro to Serial Transceivers

April 2010 What is a Transceiver?

• Transmitter converts CMOS/TTL levels to Electrical Interface Standards • Receiver converts Electrical Interface Standard levels to CMOS/TTL outputs

Electrical CMOS/TTL Transceiver Interface Standards

2 What are Electrical Interface Standards?

• Definition of electrical characteristics in order for two or more systems or equipment to communicate • Electrical Interface Standards • TIA/EIA • RS-232, RS-485 RS-422, RS-423, RS-449 • PROFIBUS • ITU-T • V.10, V.11, V.28, V.35, V.36, X.21

3 RS-232 (EIA-232) Standard

• Single-ended • Point-to-point • Output driver voltage: ± 7V typical with 5KΩ load • Receiver input voltage: ± 3V minimum • Distance of up to 15 meters • 115.2 kbps maximum data rate • Currently RS-232 Transceiver max data rate is 1 Mbps

4 RS-485 (EIA-485) Standard

• Differential • Point-to-multipoint • Up to 32 drivers and 32 receivers • 10 Mbps maximum data rate up to 50 meters • 200 kbps data rate up to 1200 meters • -7V to +12V common mode input voltage range

5 RS-422 (EIA-422) Standard

• Differential • Point-to-multidrop • 1 driver and up to 32 receivers • 10 Mbps maximum data rate up to 50 meters • 200 kbps data rate up to 1200 meters • -7V to +7V common mode input voltage range

6 Differential Signaling

• Signal on B is inverse of A

• Difference between VA and VB is 2X the amplitude • Improved noise rejection, speed, distance and reliability

A A Tx Rx B B

A-B

7 Differential Cancels Noise

Input • Noise and external Signal interference has equal impact on A each wire in the pair Noise is coupled onto both signals • A-B differential equally cancels out noise B • Common-mode offset (ground shift) is also cancelled A-B Diff. out

Noise is cancelled out by differential 8 Comparison of PROFIBUS and RS-485 PROFIBUS is SUPERSET of RS-485

Specification RS-232 RS-422 RS-485 PROFIBUS

Transmission Type Single Ended Differential Differential Differential Maximum Cable 15 m 1200 m 1200 m 1200 m Length Minimum Driver ±5 V ±2 V ±1.5 V ±2.1 V Output Voltage Driver Load 300 Ω 100 Ω 54 Ω 54 Ω Impedance Receiver Input 3kΩ to 7kΩ 4kΩ 12kΩ 20kΩ Resistance (min.) Receiver Input ±3 V ±200 mV ±200 mV ±200 mV Sensitivity Receiver Input −15 V to +15 V −7 V to +7 V −7 V to +12 V −7 V to +12 V Voltage Range

9 Serial Communication Standards

ITU-T • V.10 – Single Ended electrical circuits for data communication at up to 100 kbps • V.11 - Differential electrical circuits for data communication at up to 10 Mbps • V.28 - electrical characteristics for single ended double-current interchange circuits • V.35 - specifications from V.11 for the differential signals, while the control signals remain single ended. • V.36 – Modems spec. for synchronous data transmission using 60- 108 kHz group band circuits • X.21 - All signals are balanced.. Electrically the X.21 signals are the same as RS-422 • EIA-530 defines pinout on a 25 pin connector • RS-449 defines the pinout on a 37 pins connector

10 E-mail hotline: [email protected]