National Instruments FP-QUAD-510 User Manual

© National Instruments Corp.

You can configure each position counter to reset each time the 
index condition is met. An index-initiated reset resets both the 
upper and lower 16-bit registers associated with that axis. This 
is useful in applications in which only the position within one 
rotation of the encoder is important to the user. In this mode of 
operation, any count errors that occur are canceled when the index 
condition is met. 

Channels 0 through 3 (the lowest 16 bits of the position counter) 
each support a control command with one action—reset. The 
control-reset command resets the target counter. The control 
command ignores the index reset setting. This command also resets 
the upper 16 bits of the position counter.

The FP-QUAD-510 uses a timebase counter as a basis for 
determining the rate of change of position—the velocity—for each 
axis. The four velocity data registers, channels 8 through 11, 
contain 16-bit velocity data for axes 0 through 3 respectively. The 
data in each register represents the velocity of the axis in number 
of counts per microsecond. A positive number indicates motion in 
the forward direction, and a negative number indicates motion in 
the reverse direction. Each register can be independently 
programmed with one of eight velocity ranges as shown in Table 2. 
Each range is based on a different timebase length and has a 
different resolution. 

While the ranges available reach speeds of 

160 counts per microsecond, the module inputs are still 
limited to 1,000,000 counts per second (1 count per 
microsecond) maximum. The higher ranges are used to 
measure velocity over shorter timebases. With these 
ranges, the velocity data is averaged over a much shorter 
time period and, therefore, is more instantaneous. 
However, the data from these ranges has a coarser 
resolution. The slower ranges have a finer resolution, but 
the data is an average velocity over a longer period 
of time.