Allen-Bradley MicroLogix 1200 Reference Manual page 311

Data Table Address
This variable defines the starting address in the local controller. Valid file
types for the Data Table Address are shown below:
Message Read
Bit (B)
Timer (T)
Counter (C)
Control (R)
Integer (N)
Long Word (L)
(1) Applies to MicroLogix 1200 Series B and later, and 1500 Series B and later only.
(2) 485CIF write ST-to-485CIF only.
(3) 500CPU write RTC-to-Integer or RTC-to-RTC only.
Size in Elements
This variable defines the amount of data (in elements) to exchange with
the target device.
The maximum amount of data that can be transferred via a MSG
instruction is 103 words (206 bytes) and is determined by the destination
data type. The destination data type is defined by the type of message:
read or write.
• For Read Messages: When a read message is used, the destination file
is the data file in the local or originating processor.
Input, output, string, and RTC file types are not valid
NOTE
for read messages.
• For Write Messages: When a write message is used, the destination file
is the data file in the target processor.
The maximum number of elements that can be transmitted or received are
shown in the following table. You cannot cross file types when sending
messages. For example, you cannot read a timer into an integer file and
you cannot write counters to a timer file. The only exceptions to this rule
are that:
• long integer data can be read from or written to bit or integer files,
and
• RTC files can be written to integer files (MicroLogix 1200 Series B and
later, and 1500 Series B and later only).
Communications Instructions
Message Write
Output (O)
Input (I)
Bit (B)
Timer (T)
Counter (C)
Control (R)
Integer (N)
Long Word (L)
(1)(2)
String (ST)
(1)(3)
Real-Time Clock (RTC)
Publication 1762-RM001C-EN-P
21-11