Omron SYSMAC C2000H Operation Manual page 30

IR Area
Rack Changes
! Caution
Word Reservations
22
the right of the Master. If 18 words we required by the Units on the Slave
Racks, the first word allocated to the Unit to the right of the Master would be
IR 35.
I/O word allocations for other Remote I/O Units are not according to the
mounting order of their Master. They are determined, rather, by the word set-
ting on the Unit and the word multiplier set for the Master through which they
are controlled, according to the following equation.
Allocated word = word setting + (32 x word multiplier)
Word allocations for Remote I/O Systems are described in more detail in the
Wired and Optical Remote I/O System Manuals.
Once Units have been mounted and the I/O Table Registration operation has
been performed, a change to any Unit mounted to a Rack that affects the
type of I/O word, or the number of words, required by the Unit will cause an
I/O verification error to occur. This includes adding Units to previously un-
used slots or removing Units that have already been allocated word(s). A
Unit can, however, be replaced with another Unit that requires the same
number of input words and the same number of output words without gener-
ating an I/O verification error.
There are two ways to change the I/O table registered in memory. One is to
allocate words to a slot that is not currently being used. This method is de-
scribed below in Word Reservation.
The other way is to perform the I/O Table Registration operation again. When
this is done, all I/O words will be reallocated according to the Units mounted
to the Racks at the time. If the number of words allocated to any one slot
changes, all word allocations past that slot will also change, requiring that the
program be changed to allow for this.
Sometimes program changes can be avoided when a Unit is removed from a
Rack by reserving words. Although designed to enable slot reservations for
future use, a slot reservation can be left permanently to prevent what could
be extensive program changes.
Always be sure to change word and bit addresses in the program whenever a
change to Units on a Rack affects word allocations. Failure to do so may cause
improper I/O operations.
Words can be reserved at a certain slot for future use either by mounting a
Dummy I/O Unit to the slot before performing the I/O Table Registration op-
eration or by performing an I/O Table Change operation after performing the
I/O Table Registration operation.
A Dummy I/O Unit provides settings to designate word types (input or output)
and length (one, two, or four words). After I/O Table Generation has been
performed and a Dummy I/O Unit has been allocated the words designated
by these settings, it can be replaced at any time with a Unit that requires the
same type and number of words, e.g., if a Dummy I/O Unit is set for two input
words, it can be replaced with any 24- or 32-point Input Unit or any other Unit
that requires two input words.
Once an I/O table has been registered, it can be changed using the I/O Table
Change operation described in Section 7 Program Input, Debugging, and
Execution. This operation can be used to reserve up to four input words, out-
put words, or non-defined words at a time. It cannot be used to reserve
words for Units in Remote I/O Systems or for Interrupt Input Units.The I/O
Section 3-3