Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 149)

Formatting and Interpreting Data Blocks
Chapter 7
7Ć67
Bit 3 Search Home
In the manual mode, turn on bit 3 to generate a search-home command.
When you issue the search-home command, the servo positioning
assembly moves the axis in the direction you specify by bit 7 of the
second control word for the axis (search home direction) and at the speed
specified by bit 14 of the second motion control word (jog speed select,
high or low). The axis keeps moving until it activates the home limit
switch. When the axis trips the home limit switch, it decelerates to zero,
then proceeds at the low jog rate to the position at which the first encoder
marker occurs. If the axis cannot decelerate to zero velocity at the first
marker location, it decelerates past it, stops, then returns to the marker
location. This marker location is the axis home position. When the axis
reaches its home position, the servo positioning assembly assigns the
value in the home position words of the parameter block as the current
position.
For a firmware revision F or earlier 1771-ES expander, at power-up, the
axis must be positioned at least one encoder revolution away from the
home-limit-switch transition before you issue a search-home command
(so that a marker can be found before the switch transition). Otherwise,
the switch transition will cause a slide stop without establishing a home
position.
For a firmware revision G 1771-ES expander, if you issue a search-home
command while the home limit switch is closed, the axis first moves away
from the home limit switch until the switch has opened and the first
market has been found or one encoder revolution has been completed.
Once this occurs, the 1771-ES expander decelerates the axis to zero; then
if the marker was found, it executes the search home command by moving
the axis toward the limit switch to establish home position. However, at
power-up, if the home limit switch is open, position the axis at least one
encoder revolution away from the home limit switch before issuing a
search-home command (so that a marker can be found before the switch
transition).
If, while executing a search home command, the axis encounters a
software travel limit before it reaches the home limit switch, the servo
positioning assembly: