ASCII
13
RS485/RS232 Communications Interface
Programmer’s Information
ASCII (American Standard Code for Information Interchange)
The RS485 Option communicates using ASCII, a binary code which represents letters, digits,
and control signals (collectively called characters).
The code, originated by the American National Standards Institute (ANSI), has become a world-
wide standard for information interchange. It uses a seven bit binary word to represent all the
letters, digits, punctuation marks and control signals.
Handling of Numerical Data
(Format 21 - Free Format Numeric)
Numerical Data is transferred as a string of characters. The drive will accept any format but will
transmit an interpreted value that always contains a decimal point, and with no trailing zeros i.e.
1.00, 1.0, 1. or 1
is interpreted as
1.
-2.20 or -2.2
is interpreted as
-2.2
Handling of Status Information
(Format 23 - Hexadecimal)
Status Information is transmitted by first encoding the data into a hexadecimal format. The
length of a string is then determined by the number of characters in the encoded data. The
hexadecimal data is preceded by a ‘
>
‘ sign to differentiate it from numerical data.
Note:
Hexadecimal refers to the common practice of counting to the base of 16 in computing
rather than the base of 10. The sixteen `numbers’ used being 0 to 9, A to F. Thus an 8
bit byte is represented by two characters in the range 00 to FF, while a 16 bit word is
represented by four characters in the range 0000 to FFFF.
Block Check Character (BCC)
This is a checksum value generated by taking the exclusive OR (XOR) of the ASCII values of
all the characters transmitted after and excluding (STX) up to and including (ETX). For
example, the shaded characters are included in the (BCC) of the following message:
(EOT) (GID) (GID) (UID) (UID) (STX) (C1) (C2) (D1) (D2) (D3) (D4) (D5 (ETX) (BCC)
Example 1: EI Bisynch Prime Set
For Beginners:
You can calculate this easily by converting the ASCII values to
Binary and progressively adding the Binary values together,
obeying the following rules:
Referring to Example 1 on page 23, the calculation of (BCC) becomes:
As Characters
HEX
ASCII
Binary
(C1)
49
I
0 1 0 0 1 0 0 1
(C2)
49
I
0 1 0 0 1 0 0 1
(D1)
3E
>
0 0 1 1 1 1 1 0
(D2)
32
2
0 0 1 1 0 0 1 0
(D3)
36
6
0 0 1 1 0 1 1 0
(D4)
35
5
0 0 1 1 0 1 0 1
(D5)
30
0
0 0 1 1 0 0 0 0
(ETX)
03
(ETX)
0 0 0 0 0 0 1 1
(BCC)
3C
<
0 0 1 1 1 1 0 0 (TOTAL)
0
0
0
+
1
1
0
+
1
0
1
+
0
1
1
+
Summary of Contents for 6513
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