Rockwell Automation 1734-485ASC POINT I/O ASCII User Manual - Manual (Page 44)

Publication 1734-UM009B-EN-P - July 2003
2-18 Configuring Your ASCII Module
Setting Up and Using Delimiter Operation
When receiving data strings from your serial device, the ASCII module
can take advantage of both Start and Stop (End) delimiters. The Start
Delimiter is the start-of-string indicator and the End Delimiter is the
end-of-string indicator.
When you select Start Delimiter operation, you define a character that
prompts the ASCII module to start storing the incoming data string. All
characters up to this Start Delimiter (after the previous message was
completed) are ignored. Once the Start Delimiter is received, all
characters are stored until either the End Delimiter is received or the
Max_Receive_Char_Length is reached. Once the End Delimiter is
reached, the data string is updated and the ASCII module will ignore
all subsequent data until the start delimiter is received again.
If either delimiter is used, you also can elect whether or not to include
those characters in the data string. If the start delimiter mode is set to
Disabled, then the ASCII module will always add data to the string.
Receive String Data Type
Receive String Data Type is the format of the data – array, short_string
or string – you will send to the DeviceNet master. Which one you
choose depends on your application, and will modify the format of
the header field in the data string.
The Array data type does not have a length associated with it. It is
equivalent to specifying a length of zero using a String or Short_String
data type.
The Short_String data type is the default data type of the device. This
will suffice for most applications. The Short_String data type value has
only one byte of length, and the rest of the data bytes are appended
after the length.
The String data type value has two bytes of length. The String data
type is useful in talking to some PLCs or other devices that have a data
file specifically made to handle this data type. The length is little
endian (low byte, high byte), and the high-order byte will always be
set to zero. The ASCII module will receive up to 128 bytes of
information, so the extra byte, although required for this data type, is
always 0. Refer to Tables 2.4 through 2.6 below.