Rockwell Automation 57C422B 2 Axis Servo Module - Manual (Page 43)

PROGRAMMING 4-15
4.20 Registers 25, 26: Gear Ratio
Registers 25,26 contain the gear ratio between the feedback
and gearing reference axes. This value is read by the module
whenever the "enable gearing" (register 65) or "change gear
ratio" (register 67) command is issued. Refer to figure 4.19.
The gear ratio calculation method depends on the value of
"gear ratio format" (R38, b2). If this bit is equal to 0, the value
can be calculated with the following equation:
Gear Ratio = (feedback axis travel) * 16777216
gearing reference axis travel)
If R38, b2 is set, the gear ratio is the ratio of two 16-bit
numbers in registers 25 and 26. Register 25 is the
numerator. Register 26 is the denominator. The denominator
cannot be a negative number or 0.
If the result of the calculation is a repeating fraction, e.g., 1/3,
the module will keep track of all remainders for internal
gearing calculations. The allowable ratio range is 127:1 to
1:32767.
Note that if the gearing bit mode is set (R65, b1) and any
illegal condition is present in registers 25,26, gearing is not
enabled. If gearing is already enabled and a "change gear
ratio" command is issued (R67, b3), with illegal parameters
in registers 25,26, an illegal command fault will result.
4.21 Register 27: User LEDs
Register 27 is used to drive the three user controlled LEDs
on the faceplate of the module. These bits are read by the
module only when the "update LEDs" (register 66) command
is issued. Register 2075 (Y axis) can be used to update the
Figure 4.19 – Gear Ratio Registers