Rockwell Automation 1734-SSI POINT I/O Synchronous Serial Interface Absolute Encoder Module User Manual - Manual (Page 32)

Publication 1734-UM007D-EN-P - December 2005
4-4 Set and Operate Your Module
Operation of the Data Latch
and Comparator Features Read this section for information about operation of the Data Latch
and Comparator features.
Data Latch
See the table for a listing of values for DeviceNet name, RSLogix 5000
tag, and RSLogix 5000 field name.
SSI sensor positions can be stored with operation of the digital input
(I1). The I1 input is sourcing (IEC Type 3 compatible); thus grounding
the input turns it ON. The yellow I1 LED on the front of the SSI
module also illuminates when the I1 input is ON.
The I1 input is edge-sensitive: the module can react to rising or falling
edges of I1. Choosing the falling data latch value provides OFF-to-ON
data latching, and choosing the rising value provides ON-to-OFF
latching. Choose the Both value if you need OFF-to-ON and
ON-to-OFF data latching simultaneously.
With one of the Latch Input modes active, watch the module Status
Word (status bytes 0 and 1) for I1 input operation. When I1 is ON, bit
I1 in Status Byte 0 (bit 0 of Status Byte 0) is 1. If I1 is OFF, the I1 bit is
0. When the I1 input is activated corresponding to the Latch Input
mode, the current SSI sensor value is stored in produced bytes 4 to 7.
The LHON bit (bit 4 of Status Byte 1) will be set to 1. To unlatch the
stored value, toggle (set to 1 for about 0.5 ms, then back to 0) the
LACK bit, which is bit 0 of the Master Ack Byte. The Master Ack Byte
is consumed Byte 0 sent by the master to the 1734-SSI module. Once
the LACK bit is toggled, LHON is set back to 0 and the produced bytes
4 to 7 return to 0 as well. You can also unlatch stored data by turning
the Latch Input parameter OFF through the configuration. The LHON
bit returns to 0 as well when the Data Latch is turned OFF through the
configuration.
Data Latch
DeviceNet Name RSLogix 5000 Tag RSLogix 5000 Field Name
Bit 0 of Status Byte 0 Input InputStatus
LHON: Input DataLatched
LACK Output LatchAck