Impulse PCW-5181 user manual Appendix B Impulse Advanced Programming, Communications Protocol

Appendix B - Impulse Advanced Programming

Appendix B - Impulse Advanced Programming

The purpose of this section is to provide the information necessary for the user to communicate with an Impulse drive over a serial connection without using IDC Application Developer. Since the Impulse communications protocol is not ASCII character based, the terminal window in IDC Application Developer and terminal emulation programs such as Windows™ HyperTerminal are not compatible for use with the Impulse drive. Therefore, the topics covered here are considered advanced and require the user to understand how to directly interface with a PLC or PC serial port through programming (i.e. C or C++) or a MMI / soft PLC software package.

Communications Protocol

Transmission Frame

The Impulse drive does not use the ASCII character set for encoding and parsing serial data but rather transmits actual numeric data in the form of bytes. This convention allows for faster and more efficient serial communications by reducing the number of bytes required for data transmission and eliminating the need to convert ASCII character strings into raw data. Therefore, data references from this point forward represent actual numbers not ASCII text. For example, a ‘1’ means a value of 1 not the ASCII text character ‘1’.

The core of the Impulse communication protocol consists of a series of bytes called the transmission frame. The structure of the transmission frame is as follows:

BYTE #1	BYTE#2	BYTE#3…#n	BYTE #n+1	BYTE #n+2
Unit	Parameter	Data	Checksum	Checksum
Address	Index	Bytes	Lower Byte	Upper Byte

Unit Address

This byte specifies the address of the unit for which this transmission frame is intended. The valid range for the unit address is 1 to 255 and the factory default address is 1.

Parameter Index

This byte specifies the index of the parameter to be written to or read from. Parameter reads and writes are determined by the state of the most significant bit of the parameter index byte. If the bit is zero, the transmission frame is designated as a write. If the bit is one, the transmission frame is designated as a read. The valid range for the parameter index is 1 to 127 for writes and 129 to 255 for reads. For example, if BYTE #2 in the transmission frame equals 5, this would define a write to parameter index #5 however, if BYTE #2 equals 133, this would define a read from parameter index #5. A parameter index can be converted to a read by simply taking the index and adding 128, thus setting the most significant bit to 1.

Data Bytes

These bytes specify the data to be written to or read from the parameter index. All parameter index data is in word format (2 bytes) with the least significant byte preceding the most significant byte. Therefore, the smallest number of data bytes is 2.

Checksum Bytes

These bytes contain the unsigned sum of the Unit Address, Parameter Index and Data Bytes. These bytes are using for transmission integrity verification.

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