Rockwell Automation 1771-IJ_IK IK ENCODER/COUNTER MODULES - Manual (Page 33)

5–3 Single Transfer Programming
Publication 1771ĆUM006B-EN-P - June 2002
Note that if a device is wired to channel B for external control of
count direction, the up/down bit must be set to 1. Count direction
can be externally controlled by using a transistor switch, as described
in chapters 2 and 3.
Bit 12 is the enable outputs bit. The state of this bit controls module
outputs as follows:
1 -Outputs enabled. This means that the output module can be
energized based on logical operations performed by the module.
0 -Outputs disabled. This means that the outputs of the module
cannot be energized.
With bit 12 set to 1, the module can energize its output terminals
based on a comparison of its accumulated count and preset values set
by the program.
Bits 10 and 11 are termed function control bits. These bits control
module function in both encoder and counter modes. They permit
the counting operation of the module to be enabled or reset by the
program. The table in Figure 5.1 shows the bit settings for each
function.
Bit 07 is the home latch enable bit.
The module resets the count to zero only when all three of these
conditions are true:
•
Home latch enable bit (bit 07) is set to 1.
•
Marker input is high.
•
Home limit switch is closed (limit switch LED is on).
The count remains at zero until one or more of these conditions go
false. Then module operation follows the function control bits
described in Figure 5.1.
The module indicates it has reset its count to zero by setting the
home bit (bit 17 in the input status word). It resets this bit when the
home latch enable bit (bit 07) is reset. (Refer to Figure 4.2, Input
Status Word).
The system can bring the machine back to a repeatable starting
position, and the module count can be reset to zero by toggling either
the marker input or home limit switch rather than changing bits 11
and 10 in the control word as long as the three conditions are met.
Carry and borrow bits are not affected by resetting the module count.
The home limit switch LED turns on whenever the home limit
switch is closed.