Electro Cam PS-6144 Series - Manual (Page 75)

6-3 Communications
Serial Communications Using Electro Cam Corp. Protocol (Standard 6144 Units)
Background PS-6144 controllers include programming that allows them to accept and respond to a
set of serial commands issued by a system host such as a PLC or other computer. The
commands can interrogate the PS-6144 for operating and control data, and they can
also change programming values within the PS-6144.
Serial communications are initiated when the system host sends a command to the PS-
6144. The PS-6144 processes the command and sends a reply to the host. Modbus
ASCII protocol is available (see page 6-16).
Syntax All commands are sent and received as ASCII character strings in the following syntax.
Do not include spaces between fields.
Command from Host: STX ADR CMD <DTA> CSM ETX
Reply from PLuS: ACK or NAK <DTA> CSM ETX
No. of
Field Characters Description
STX 1 Start of text. The PLuS uses “!” for this character.
ADR 2 hex Address of PLuS controller on network (0-255)
CMD 2 hex Command number. Commands are listed later in this chap-
ter.
DTA n hex The number and type of data elements is determined by the
command, reply, or the error.
All data is sent and received in hex.
CSM 2 hex Checksum. The method by which the PS-6144 calculates
the checksum is described later in this chapter. When the
host sends a command, it must include a checksum calcu-
lated in the same way so that the PS-6144 can check the
command for communication errors. The host should also
use this calculation method to analyze the reply from the
PS-6144 for possible communication errors.
ETX 1 End of text. The PLuS uses a carriage return, or <CR>, for
this character
ACK 1 Positive acknowledge. The PLuS uses the letter “A” for ACK.
NAK 1 Negative acknowledge, or error condition. The PLuS uses
the letter “N” for NAK. A list of error replies are included later
in this section.
The specified number of ASCII characters must be sent for each field. Include leading
zeroes if the data in a field is less than the field length. The control will also include
leading zeroes in its replies.