485SDD16-1005 Manual
9
B&B Electronics -- 707 Dayton Road -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
Chapter 3 - Commands
There are only two commands required to control the 485SDD16:
set output lines, and read I/O lines. Five additional commands are
used for configuring the module: set module address, set turn-
around delay, define I/O lines, set power-up states, and read
configuration. Command strings are from four to six bytes in length:
the “!” character, an address byte, two command characters, and
one or two data bytes (if required). (See Table 3.1).
Table 3.1 - 485SDD16 Commands
Function Command
Response
Read I/O Lines
!{addr}RD
{I/O msb}{I/O lsb}
Set Output Lines
!{addr}SO{I/O msb}{I/O
lsb}
no response
Set Module Address
!{addr}SA{new adr}
no response
Set Turn-around
Delay
!{addr}SC{#} no
response
Define I/O Lines
!{addr}SD{I/O msb}{I/O lsb} no response
Set Power-up States !{addr}SS{I/O msb}{I/O lsb} no response
Read Configuration
!{addr}RC
I/O Definitions
{I/O msb}{I/O lsb}
Power-up States
{I/O msb}{I/O msb}
RS-485 Config.
{addr}{t-a delay}
Symbols: {...} represents one byte
<...>
represents
a
numeric
value
Before going into the specifics of each command, it is important
to understand that a byte has a numeric value from 0 to 255. The
byte's value can be represented in decimal (0 - 255) format,
hexadecimal (00 - FF) format, binary (00000000 - 11111111) format,
or as an ASCII character. The fixed bytes of each command will be
represented as ASCII characters. For example the Read I/O
command contains the following ASCII characters: “!" and "RD”.
Refer to Table 3.1. However, it is important to remember that an
ASCII character has a numeric value. Example: the ASCII "0" (zero)
does not have a numeric value of zero but has a value of 48. The
decimal and hexadecimal equivalents of some ASCII characters are
shown in Table 3.2. Some commands require additional data bytes
to complete the command. These data bytes may be represented in
any of the formats list above. Refer to Appendix A for more ASCII
and decimal equivalents.
10 485SDD16-1005
Manual
B&B Electronics -- 707 Dayton Road -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
Table 3.2 - Equivalent Values
ASCII Decimal Hexadecimal
! 33 21h
0 48 30h
A 65 41h
C 67 43h
D 68 44h
O 79 4Fh
R 82 52h
S 83 53h
Syntax
Command strings consist of four to six bytes. The first byte is the
start of message byte. The start of message byte is always the
ASCII “!” character. The second byte is the address byte. This byte
allows each unit to have a unique address. The factory default
address is the ASCII "0" character. The next two bytes are the
command characters. These bytes are ASCII characters and used
to specify which command will be executed by the module. Some
commands require an argument field containing a fifth and
sometimes a sixth data byte. Commands that manipulate I/O lines
require two data bytes, a
M
ost
S
ignificant and a
L
east
S
ignificant
data byte respectively.
Command Syntax:
!
0
_
_
_
_
| | | | | |
|
|
|
|
| 6th Data Byte
| | | |
5th
Data
Byte
| | | 2nd
Command
Byte
|
|
1st Command Byte
| Address
Byte
Start
of
Message
Byte
I/O Data Bytes
When constructing commands to manipulate output lines or
when reading the state of the I/O lines it is necessary to know how to
select and interpret the I/O data bytes. The sixteen I/O lines are
represented by two data bytes. The Most Significant data byte
represents I/O lines #15 through #8 and the Least Significant data
byte represents I/O lines #7 through #0. The Most Significant byte is
always sent and received first followed by the Least Significant byte.
