Serial communications

This section covers serial communications on SPLat controllers. Originally SPLat had a single serial port, and it was intended primarily for programming via SPLat/PC. It can however also be used for communicating with 3rd party devices. In modern terminology a serial port is often referred to as a COM port, a term adopted from personal computers.

More recently designed SPLat controllers have more than one serial port, particularly 32-bit designs.

Serial communications between any two devices requires that there be agreement on two major things:

The electrical interface

The electrical interface defines the voltage levels, pinouts etc of the electrical connection. Common standards are RS232 and RS485.

Some SPLat controllers have RS232 compatible serial interfaces. Others (the models that use our special programming cable) do not, but can be converted to RS232 via a programming cable.

We have a range of RS485 adaptors available, so all SPLat controllers can potentially provide RS485.

Newer designs have a USB programming port.

The protocol

The protocol is the "language" used to convey information across the electrical interface. Just like all people use essentially the same repertoire of sounds interface to each other, there are many different, mutually incompatible, languages.

SPLat controllers support:

• Our proprietary protocol, SPLatLink, which is used by SPLat/PC for programming and debugging. It is no longer supported as a protocol for user applications.
• ModBus, which is one of the oldest and most common industrial protocols. SPLat supports "ModBus RTU, master and slave". The majority of commonly used ModBus "functions" are supported.
• "User programmable" protocols. SPLat contains a fairly open-ended facility for generating and decoding (parsing) the kinds data messages and commands used by a lot of 3rd party devices such as weigh scales, motion controllers, laboratory instruments etc.
• Other specialised protocols that are implemented using Hash commands and functions. These fall technically under the heading of user programmable protocols, but have been nicely packaged in a "hash programming" wrapper to make them very much easier for you to use. Examples include SimpleHMI.

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Related topics

Debugging using serial data and the terminal function in SPLat/PC SimpleHMI