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RS232/422/485

RS232/422/485 asynchronous communication has been around for a long time. PCs used to have a RS232 port as a standard feature. Today, if you need to interface with equipment that has a RS232/422/485 serial port, you will need to add a RS232/422/485 port or ports to your PC, server, laptop, smartphone or tablet. See the pros and cons of RS232 versus RS422/485.

There are a number of ways of achieving this.

  • PCs and Servers: Plug in PCI or PCI Express cards that can provide 1 to 16 ports per card. The number of cards is limited by the number of free slots available. Interfacing using RS232/422/485 cards gives the lowest latency of all methods. Latency is the time taken to produce the RS232/422/485 signals.
    All computers with a USB interface: You can use a USB to serial RS232/422/485 converter. These are available from 1 to 32 ports per unit. This is a very popular method as it does not involve opening the PC.
  • Networks and Internet: Interfaces are available for both wired and WiFi Ethernet. One to sixteen RS232/422/485 ports can be interfaced across the network or World Wide Web. A “modem tunnel” is possible with an Ethernet to serial converter at both ends of the network.
  • Bluetooth: Very useful when cables need to be eliminated. It is the best method for connecting RS232 devices to tablets and smartphones.
  • Mobile Phone Networks: Remote serial RS232/422 equipment can be monitored and controlled wherever there is mobile phone coverage. Interfaces can have two SIM cards to switch between networks.

The difference between RS232 RS422 RS485

 RS232RS422RS485
Cablingsingle endedSingle ended multi-dropmulti-drop
Number of Devices1 transmit,1 receive1 transmitter, 10 receivers32 transmitter, 32 receivers
Comms Modefull duplexfull duplex, half duplexfull duplex. half duplex
Max Distance50 feet at 19.2Kbps4000 feet at 115Kbps4000 feet at 115Kbps
Max Dada Rate for 50 feet1Mbps10Mbps10Mbps
Signallingunbalancedbalancedbalanced
Mark (data1)-5V min -15V max2V min 6V max1.5V max
Space (data 0)+5V min +15V Max2V min 6V max1.5V max
Input Level Min+/- 3V0.2V difference0.2V difference

CAN Bus

The Controller Area Network (CAN or CAN-Bus) has been invented for use in vehicles (cars, trucks) to reduce the complexity of the cabling systems and to allow the control of different sensors and devices. Because of its reliability against noise and transmission errors the CAN-Bus is also used as an industrial “Fieldbus”. Today CAN-Bus is mainly used to control factory automation for many different controlling and data acquisition applications.

CAN-Bus is a broadcast bus with differential serial data transmission, where the bits are being sent in NRZ coded frames. The frames consist of an ID to identify the sender type and up to 8 data bytes, the frame is sensed from all CAN-bus nodes. A CAN network can be configured to work with two different frame formats: the standard frame format has a 11 Bits ID (CAN 2.0A) whereas the extended frame format uses 29 Bits ID (CAN 2.0B). CAN-Bus features an automatic ‘arbitration free’ transmission. A CAN message that is transmitted with highest priority will ‘win’ the arbitration, and the node transmitting the lower priority message will sense this, back off and wait.

Using the VScom CAN adapters a PC can be connected to the CAN Network in a simple manner: over USB, over a serial port, over Ethernet or over a PCI Add-on card. All VScom CAN adapters support both CAN 2.0A and CAN 2.0B frame format to fulfil the task of controlling and monitoring. The PC can in the same time additionally log the data and status of the CAN-bus, without interfering with the control application.

CANHacker, a tool for analysing and transmitting frames on the CAN BUS, is included in the product package.

MOD Bus

Modbus Protocol is a messaging structure developed by Modicon in 1979. It is used to establish master-slave/client-server communication between intelligent devices. It is a de facto standard, truly open and the most widely used network protocol in the industrial manufacturing environment. It has been implemented by hundreds of vendors on thousands of different devices to transfer discrete/analog I/O and register data between control devices. It’s a lingua franca or common denominator between different manufacturers. One report called it the “de facto standard in multi-vendor integration”. Industry analysts have reported over 7 million Modbus nodes in North America and Europe alone.