Allen-Bradley 1779-KFMR User Manual page 121

Protected Write Block
Use this command to write a block of data into limited areas of data table
memory in a programmable controller. Your access can be limited by
memory access rungs in the communication zone of the controller's
ladder-diagram program. If the program contains no memory access
rungs, this command operates the same as an unprotected write block.
Use the address (L ADDR) field to specify the starting logical byte
address for where to write this block of data.
Command Format:
Success Reply Format:
Unless otherwise stated, values shown are in hexadecimal, and each block
shown represents one byte.
Unprotected Write Bit
Use this command to set or reset specified bits within specified bytes
within any area of data table memory in a programmable controller.
The fields following the TNS field consist of up to 61 four-byte blocks,
each of which contains a two-byte logical-address field, a one-byte
set-mask field, and a one-byte reset-mask field. Each 1 in a set-mask field
sets the corresponding bit to 1. Each 1 in a reset-mask field resets the
corresponding bit to 0. Those bits within the byte, but not designated by a
1 in either the set or reset mask, remain unchanged.
The interface at the receiving node executes this command by first
making a copy of the addressed controller byte. It sets the bits specified
in the set mask, then resets the bits specified in the reset mask, and then
writes the byte back into controller memory. At the same time, the
controller can be changing the states of the original bits in memory.
Because of this, some data bits may unintentionally be overwritten. To
help prevent this, we suggest you use this command to write into the
Chapter 8