Emerson Digistart CS, User Manual

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10
Modbus Module User Guide
www.controltechniques.com Issue 1
6. AP ASCII Protocol
The message fragments used to communicate with the Modbus Module as an AP ASCII slave device are shown below. The message
fragments may be assembled into complete messages as described in the sections that follow.
NOTE
Data must be transmitted in 8-bit ASCII, no parity, one stop bit.
Table 6-1 AP ASCII message fragments
Message Fragment Type ASCII Character String or
(Hexadecimal Character String)
Send address EOT
(04h [nn]
[nn] [lrc]
[lrc] ENQ or
05h)
Send command STX [ccc] [lrc] ETX or
Send request (02h [ccc] [lrc] 03h)
Receive data STX
(02h [dddd]
[dddd] [lrc]
[lrc] ETX or
03h)
Receive status STX
(02h [ssss]
[ssss] [lrc]
[lrc] ETX or
03h)
ACK (acknowledge) ACK
(06h) or
NAK (negative acknowledge) NAK
(15h) or
ERR (error) BEL
(07h) or
nn = two byte ASCII number representing the soft starter address where each decimal digit is represented by n.
lrc = two byte longitudinal redundancy check in hexadecimal.
ccc = three byte ASCII command number where each character is represented by c.
dddd = four byte ASCII number representing the current or temperature data where each decimal digit is represented by d.
ssss = four byte ASCII number. The first two bytes are ASCII zero. The last two bytes represent the nibbles of a single byte of
status data in hexadecimal.
6.1 Commands
Commands can be sent to the soft starter using the following format:
Figure 6-1 Command format
Send
address
ACK Send
command
ACK
Possible error responses: NAK (Invalid LRC)
= Master = Slave
(soft starter)
Command ASCII Comment
Start B10 Initiates a start
Stop B12 Initiates a stop
Reset B14 Resets a trip state
Quick stop B16 Initiates an immediate removal of voltage from the motor. Any soft stop settings are
ignored.
Forced communication trip B18 Causes a communications trip