B&B Electronics RS-232 Digital I/O Module 232SDD16 - Manual (Page 7)

232SDD16-1005 Manual 9
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
Chapter 3 - Commands
There are only two commands required to control the 232SDD16:
set output lines, and read I/O lines. Three additional commands are
used for configuring the module: define I/O lines, set power-up
states, and read configuration. Command strings are from four to
six bytes in length; the “!” character, the “0” (zero) character, two
command characters, and one or two data bytes, if required. (See
Table 3.1).
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: “!0RD”. 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 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 listed above. Refer to Appendix A for more ASCII
and decimal equivalents.
Table 3.1 - 232SDD16 Commands
Function Command Response
Set Output Lines !0SO{I/O msb}{I/O lsb} no response
Read I/O Lines !0RD {I/O msb}{I/O lsb}
Define I/O Lines !0SD{I/O msb}{I/O lsb} no response
Set Power-up States !0SS{I/O msb}{I/O lsb} no response
Read Configuration
!0RC I/O Definitions
{I/O msb}{I/O lsb}
Power-up States
{I/O msb}{I/O msb}
Symbols: {...} represents one byte
<...> represents a numeric value
10 232SDD16-1005 Manual
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
Syntax
Command strings consists 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 (useful in RS-485
networks). Since the 232SDD16 uses RS-232 communications, this
byte is always the ASCII “0” character and can not be changed. 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. This field
contains the fifth and sixth data byte, a Most Significant and a Least
Significant 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 outputs 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.
Table 3.2 - Equivalent Values
ASCII Decimal Hexadecimal
! 33 21h
0 48 30h
C 67 43h
D 68 44h
O 79 4Fh
R 82 52h
S 83 53h