Interface Types and Interface Converters Explained

There are numerous interface types developed for various applications for data and signal transportation. We will cover RS232, RS485, RS422, SPI, CAN, DigRF etc. Each of these types have unique specifications and hence interface converters are used to support applications one is not designed for. For example there are two devices one work on RS232 and the other on RS485. To allow communication between these two devices we need a converter (RS232 to RS485).

RS232 Interface

• A serial communication standard used to connect computers and peripherals.
• It is point to point.
• Logic ‘1’ and ‘0’ are represented by voltage polariy and not level.
• Support distance of about 15 meters and speeds up to 115 kbps
• Applications : Serial ports (COM ports), modems, old mouse and keyboard connectivities
• Advantages : Simple, widely supported
• Disadvantages : Short range, noisy at higher speeds

RS485 Interface

• It is differential version of serial communication which supports multiple devices on same bus.
• It is multi-point interface, supports 32 devices (Typically)
• It uses differential voltages for better noise immunity.
• It supports distance of about 1.2 Km and speeds up to 10 Mbps.
• Applications : Industrial automation e.g. Modbus, building control systems, CCTV
• Advantages : Longer distances, multiple devices, robust against noise
• Disadvantages : More complex than RS232, needs addressing

RS422 Interface

• It is similar to RS485 but only supports one driver and multiple receivers
• One way differential signaling, one transmitter and many receivers
• Supports distances of about 1200 meters at lower speeds.
• Applications : Industrial networking, military applications, instrumentation
• Advantages : Long cable lengths, excellent noise immunity
• Disadvantages : No multi-master capability

SPI Interface

• It is a synchronous serial communication protocol between a master and one or slaves
• Wiring : Requires four lines viz. MOSI, MISO, SCLK and SS
• Supports short distances (at PCB level) and very fast speeds (about tens of Mbps)
• Applications : Communicatng with sensors, SD cards, EEPROMs, displays
• Advantages : Very fast, simple hardware
• Disadvantages : More wires are required per device if not daisy chained

CAN Interface

• It is a multi-master and message based protocol designed for robustness in noisy environments
• Witing supports twisted pair and differential signaling
• Distance/Speed : Support ~ 40 meters at 1 Mbps, ~ 500 Kbps at 1 Km
• Applications : Automotive systems (ECUs, airbags, brakes), industrial automation
• Advantages : Robust error handling, priority based messaging, real time communication
• Disadvantages : More complex than basic serial interfaces

DigRF Interface

• High speed interface used mainly between baseband processors and RF ICs in mobile phones
• Supports very short distances and very high data rates (in multiple of Gbps)
• Applications : LTE/5G Mobile phones
• Advantages : Very high data rates, lower latency
• Disadvantages : Specialized applications, not used outside mobile RF communication

USB interface

• A universaL serial bus used for connectiong computers to peripherals
• Uses 4 or more wires
• Support for distances and speed vary based on USB versions, For example USB 3.0 supports ~ 3 meters and up to 5 Gbps, USB 4.0 supports up to 40 Gbps
• Applications : Almost all modern electronics
• Advantages : Plug and Play, hot swappable, supports data + Power, high speed
• Disadvantages : Limited cable length, host controlled only

Interface converters

There are different types of interfaces. To allow communication between devices having specific interfaces, we need suitable interface converters. Following are some of the main reasons why interface converters are required.

• Different electrical standards : RS232 (unbalanced) to RS485 (differential signaling)
• Different communication logic : SPI (Synchronous) to RS232 (Asynchronous)
• Distance & noise considerations : RS232 to RS485 extends communication over longer cables without errors. RS232 is good for short distances where as RS485 handles longer distances
• Multi device communication : RS232 device to talk to multiple devices via RS485 on a single bus
• Compatibility with modern systems : Many PCs do not have RS232 and only USB is available. USB to RS232 and USB to CAN converters are needed to keep using older systems
• Different data rates and framing : CAN handles message IDs and priorities where as RS232 sends simple stream of bytes.

Summary

Various interface types have been developed to support specific use cases, maximum devices, distance and speeds. Converters allow devices with different hardware, voltages, timings and protocols to communicate safely and correctly.