The Data Latch (LATx
registers) is useful for Read-Modify-Write operations on the value that the I/O pins are
driving.
A write operation to the LATx register has the same effect as a
write to the corresponding PORTx register. A read of the LATx register reads of the
values held in the I/O PORT latches, while a read of the PORTx register reads the actual
I/O pin value.
Important: As a general rule,
output operations to a port must use the LAT register to avoid Read-Modify-Write issues.
For example, a bit set or clear operation reads the port, modifies the bit, and writes
the result back to the port. When two bit operations are executed in succession, output
loading on the changed bit may delay the change at the output in which case the bit will
be misread in the second bit operation and written to an unexpected level. The LAT
registers are isolated from the port loading and therefore changes are not
delayed.