Rice Lake Allen-Bradley Remote I/O - Manual (Page 10)

6 Remote I/O Installation and Programming Manual
3.0 Discrete Transfer Commands
Discrete commands are used by the PLC to send and receive data from the Remote I/O Interface. The PLC
controller and Remote I/O Interface share a quarter rack of slot space, resulting in two 16-bit words for the output
image table (used to write commands to the indicator) and two 16-bit words for the input image table (used to
read data from the indicator).
NOTE: Data returned by discrete transfer commands is not valid when the indicator is in setup mode.
3.1 Output Image Table Format
To perform a discrete command, the PLC places two 16-bit words in the PLC output image table, which is sent
by the scanner to the node adapter of the Remote I/O Interface. The Remote I/O Interface provides the contents
of the output image table to the indicator for command processing.
The format of the output image table is shown in Table 3-1.
Table 3-1. Output Image Table Format
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Word 0 v15 v14 v13 v12 v11 v10 v09 v08 v07 v06 v05 v04 v03 v02 v01 v00
Word 1 p07 p06 p05 p04 p03 p02 p01 p00 c07 c06 c05 c04 c03 c02 c01 c00
where:
v00–v15 16-bit unsigned integer value
p00–p07 Parameter value
c00–c07 Command number
These fields are described below:
Value
Word 0 of the output image table is used to pass value
data on certain commands. This field should be used
only when block transfer is disabled. For example, to
enter a tare value, use word 0 to specify the tare value;
the Enter Tare command number (12) is specified in
bits 00 through 07 of word 1.
Values entered in this field are treated as unsigned
integers. Possible values range from 0 to 65535.
Parameter value
To allow communication with a multi-scale indicator,
the scale number is sent in the upper byte of word 1. A
value of 0 represents the current scale. Certain
commands require a parameter other than a scale
number. These commands are noted in the table as
requiring a slot number or other selection parameter.
Command Number
The number representing the indicator command is
sent in the lower byte of word 1. Table 3-2 lists the
remote commands that can be specified for
520 and
920i indicators on discrete write commands.
NOTE: A lockout feature that looks for any change in the
image table data is incorporated into the indicator receive
mechanism to prevent inundation by the same command.
Repeated commands must be separated by any other valid
command/parameter/value combination.
Decimal Hex Binary Command
0 0x00 0000 0000 Return Status and Weight
1 0x01 0000 0001 Display Channel
2 0x02 0000 0010 Display Gross Weight
3 0x03 0000 0011 Display Net Weight
4 0x04 0000 0100 Display Piece Count
9 0x09 0000 1001 Gross/Net key press (toggle mode)
10 0x0A 0000 1010 Zero
11 0x0B 0000 1011 Display Tare
12 0x0C 0000 1100 Enter Tare (integer)
13 0x0D 0000 1101 Acquire Tare
Table 3-2. 520 /720i/ 820i / 920i Remote Commands