Serial data communications

TL;DR: The fundamental definitions and basic principles of digital serial data communications are reviewed, including methods for detecting errors in communication, which is an important consideration in noisy industrial environments.

Abstract: This chapter reviews the fundamental definitions and basic principles of digital serial data communications. The chapter details two of the most popular and common interface standards used in data acquisition and control systems: RS-232 and RS-485. The RS-232 standard is designed for the connection of two devices: data terminal equipment (DTE), such as a computer or printer; and data communications equipment (DCE), such as a modem. The EIA RS-485 is the most versatile of the EIA standards, and is an expansion of the RS-422 standard. It allows up to 32 line drivers and 32 line receivers on the same line. It incorporates the advantages of balanced lines with the need for only two wires (plus signal common) cabling. RS-485 provides reliable serial communications for: distances of up to 1200 m, data rates of up to 10 Mbps, up to 32 line drivers permitted on the same line, and up to 32 line receivers permitted on the same line. This chapter also examines the most common industrial protocols, including methods for detecting errors in communication, which is an important consideration in noisy industrial environments. Troubleshooting and testing serial data communications circuits is also discussed in detail.