Serial Communications Protocol; Ansi Communications Protocol; Introduction; Physical Layer And Uart - Emerson Mentor MP Advanced User's Manual

Parameter structure Keypad and display
6 Serial communications
protocol
6.1

ANSI communications protocol

6.1.1

Introduction

Mentor MP supports an ANSIx3.28 type comms protocol as supported
by previous Control Techniques products with some modification to allow
access to 32 bit parameters. This chapter describes the implementation
of the protocol for Mentor MP.
6.1.2

Physical layer and UART

Attribute
Physical layer 2 wire EIA485
Standard UART asynchronous symbols with Non
Bit stream
Return to Zero (NRZ)
Each symbol consists of:
1 start bit
Symbol 7 data bits (ASCII)
1 parity bit (even parity)
1 stop bit
Baud rates 300, 600, 1200, 2400, 4800, 9600, 19200, 38400
6.1.3

Reading a parameter

The command to read a parameter is:
EOT End of transmission (Ctl D)
A1
Drive address: 1
A1
Drive address: 1
A2
Drive address: 2
A2
Drive address: 2
M1
Menu number: 1
M2
Menu number: 2
P1
Parameter number: 1
P2
Parameter number: 2
ENQ Enquiry (Ctl E)
If the message is correct and the parameter exists the response is:
STX Start of text (Ctl B)
M1
Menu number: 1
M2
Menu number: 2
P1
Parameter number: 1
P2
Parameter number: 2
st
D1
Data: 1 digit
nd
D2
Data: 2 digit
-
-
Dn Data: nth digit
ETX End of text (Ctl C)
Checksum
The length of the data field varies depending on the number of
significant digits required to represent the value of the parameter. The
maximum length is 12 digits including the sign and decimal point if
present. The data field always starts with a sign, minus sign for negative
numbers, or a plus sign for zero and positive numbers. The field may
contain a decimal point, but this will not be before all the numbers in the
field or after all the numbers in the field. The following examples
demonstrate some possible data fields.
188
Parameter description
Parameter x.00
Description
st
digit
st
digit
nd
digit
nd
digit
st
digit
nd
digit
st
digit
nd
digit
st
digit
nd
digit
st
digit
nd
digit
www.controltechniques.com
Advanced parameter
format descriptions
Value
0 +0 (parameter with no decimal places)
0 +0.00 (parameter with 2 decimal places)
1.2 +1.2
-345.78 -345.78
123456 +123456
If the parameter to be read does not exist the End of transmission
character (Ctl D) is returned.
The checksum is derived by exclusive ORing the message byte together
excluding the STX and the checksum, i.e. Checksum = M1 ^ M2 ^ P1^
P2 ^ D1 ^ D2 ^ ...... Dn ^ ETX. The checksum is an unsigned 8 bit value
and if the checksum is less than 32 then 32 is added to the calculated
checksum.
6.1.4

Writing to a parameter

The command to write to a parameter is:
EOT End of transmission (Ctl D)
A1
Drive address: 1
A1
Drive address: 1
A2
Drive address: 2
A2
Drive address: 2
STX Start of text (Ctl B)
M1
Menu number: 1
M2
Menu number: 2
P1
Parameter number: 1
P2
Parameter number: 2
st
D1
Data: 1
nd
D2
Data: 2
-
-
Dn Data: nth digit
ETX End of text (Ctl C)
Checksum
The following rules apply to the data field:
1. The maximum length is 12 characters.
2. The field may contain leading spaces, but not after any other
character.
3. A sign character is optional. No sign indicates positive.
4. A decimal point is optional. This can appear at any point in the data
field, but not before the sign or before 10 numbers (i.e. the value
written should not have more than 9 decimal places). If the decimal
point is not in the same position as used by the parameter some
accuracy may be lost or extra decimal places added (i.e. if +1.2345
is written to a parameter with one decimal place the result is +1.2, if
+1.2 is written to a parameter with three decimal places the result is
+1.200). It should be noted that parameters can only have 0, 1, 2, 3,
4, 5, or 6 decimal places.
5. The data field can contain up to 10 numbers, but the value even
ignoring decimal points must not exceed the range –2
If the parameter is written successfully an Acknowledge character (Ctl F)
is returned. If the parameter does not exist, the value written exceeds
the allowed parameter range or the data field rules are not obeyed an
Not acknowledge character (Ctl U) is returned.
The checksum is derived by exclusive ORing the message byte together
excluding the STX and the checksum, i.e. Checksum = M1 ^ M2 ^ P1^
P2 ^ D1 ^ D2 ^ ...... Dn ^ ETX. The checksum is an unsigned 8 bit value
and if the checksum is less than 32 then 32 is added to the calculated
checksum.
Serial comms
protocol
Data field
st
digit
st
digit
nd
digit
nd
digit
st
digit
nd
digit
st
digit
nd
digit
digit
digit
Mentor MP Advanced User Guide
Issue Number: 1
Performance
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to 2 -1.