HCTL-1100 Datasheet, PDF (24/40 Pages) Agilent(Hewlett-Packard) – General Purpose Motion Control ICs

Sample Timer Register (R0FH)
The contents of this register set
the sampling period of the HCTL-
1100. The sampling period is:
t = 16(T+1)(1/frequency of the
external clock)
[4]
where:
T = contents of register R0FH
The Sample Timer has a limit on
the minimum allowable sample
time depending on the control
mode being executed. The limits
are given in Table 4 below.
The minimum value limits are to
make sure the internal programs
have enough time to complete
proper execution.
The maximum value of T (R0FH)
is FFH (255D). With a 2 MHz
clock, the sample time can vary
from 64 µsec to 2048 µsec. With
a 1 MHz clock, the sample time
can vary from 128 µsec to 4096
µsec.
Digital closed-loop systems with
slow sampling times have lower
stability and a lower bandwidth
than similar systems with faster
sampling times. To keep the
system stability and bandwidth as
high as possible the HCTL-1100
should typically be programmed
with the fastest sampling time
Table 4.
Control Mode
Position Control
Proportional Velocity Control
Trapezoidal Profile Control
Integral Velocity Control
possible. This rule of thumb must
be balanced by the needs of the
velocity range to be controlled.
Velocities are specified to the
HCTL-1100 in terms of
quadrature encoder counts per
sample time. The faster the
sampling time, the higher the
slowest possible speed.
Hardware Description
The Sample Timer consists of a
buffer and a decrement counter.
Each time the counter reaches
00H, the Sampler Timer Value T
(value written to R0FH) is loaded
from the buffer into the counter,
which immediately begins to
decrement from T.
Writing to the Sample Timer
Register
Data written to R0FH will be
latched into the internal buffer
and used by the counter after it
completes the present sample
time cycle by decrementing to
00H. The next sample time will
use the newly written data.
Reading the Sample Timer Register
Reading R0FH gives the values
directly from the decrementing
counter. Therefore, the data read
from R0FH will have a value
anywhere between T and 00H,
depending where in the sample
time cycle the counter is.
R0FH Contents
Minimum Limit
07H(07D)
07H(07D)
0FH(15D)
0FH(15D)
Example –
1. On reset, the value of the timer
is pre-set to 40H.
2. Reading R0FH shows
3EH . . . 2BH . . . 08H . . .
3CH . . .
Synchronizing Multiple Axes
Synchronizing multiple axes with
HCTL-1100s can be achieved by
using the SYNC pin as explained
in the Pin Discussion section.
Some users may not only want to
synchronize several HCTL-1100s
but also follow custom profiles for
each axis. To do this, the user
may need to write a new
command position or command
velocity during each sample time
for the duration of the profile. In
this case, data written to the
HCTL-1100 has to be coordinated
with the Sample Timer. This is so
that only one command position
or velocity is received during any
one sample period, and that it is
written at the proper time within
a sample period.
At the beginning of each sample
period, the HCTL-1100 is
performing calculations and
executions. New command
positions and velocities should
not be written to the HCTL-1100
during this time. If they are, the
calculations may be thrown off
and cause unpredictable control.
The user can read the Sample
Timer Register to avoid writing
too early during a sample period.
Since the Sample Timer Register
continuously counts down from
its programmed value, the user
can check if enough time has
passed in the sample period to
insure the completion of the
internal calculations. The length
of time needed by the HCTL-1100
24