Rockwell Automation 57C419 5V-24V DC Input Module - Manual (Page 24)

4Ć8
7800 !
8000 LATCH RESET B19@ = FALSE
8010 B19 CNT% = B19 CNT% + 1 \!Interrupt service routine B19
9000 !
10000 END
4.5 Restrictions
This section describes limitations and restrictions on the use of this
module.
4.5.1 Writing Data to Registers
The input registers (0 and 1) on this module are read only. Attempts
to write to them will cause a bus error (severe system error). The
following are examples from programs that write to the module and
should therefore be avoided:
a.ăReferencing an input from the coil in a Ladder Logic task.
b.ăReferencing the module on the left side of an equal sign in a
ăăĂLET statement in a Control Block or BASIC task.
c.ăReferencing an input as an output in a Control Block
ăăĂfunction.
4.5.2 32 Bit Register Reference
WARNING
IF YOU USE DOUBLE INTEGER VARIABLES IN THIS INSTANCE, YOU MUST
IMPLEMENT A SOFTWARE HANDSHAKE TO ENSURE THAT BOTH THE LEAST
SIGNIFICANT AND MOST SIGNIFICANT 16 BITS HAVE BEEN TRANSMITTED
BEFORE THEY ARE READ BY THE RECEIVING APPLICATION PROGRAM.
FAILURE TO OBSERVE THIS PRECAUTION COULD RESULT IN BODILY INJURY
OR DAMAGE TO EQUIPMENT.
32 bit register references should be used with caution when this
module is placed in a remote rack. The remote I/Osystem does not
always transfer registers greater than 16 bits as a unit. As a result, it is
possible for an application program to read the least significant 16
bits of a new value and the most significant 16 bits of the previous
value as a 32 bit register reference.
4.5.3 Interrupts in Remote I/O Racks
When this module is in a remote rack, the interrupt mode cannot be
used.
4.5.4 Dynamic Modification of Latch Edge Transition
Whenever the edge transition bit is toggled, the corresponding latch
status bit will be reset, regardless of whether an interrupt was
pending. For this reason, edge transition bits should not be modified
by the user after the module has been initialized.