BitFlow Cyton-CXP, Hardware Reference Manual

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Introduction The Cyton-CXP
CYT-5-2 BitFlow, Inc. Version A.0
5.1.3 Interval Mode
Often in situations when a stage is moving back and forth, acquisition is only required
over a subsection of the total stage range. Interval mode has been designed for these
situations. When the board is in interval mode, it only acquires lines when the
encoder counter is between a lower limit and an upper limit. If the counter is outside
these limits, lines are not acquired.
To use interval mode, set QENC_INTRVL_MODE = 1, and program QENC_INTRVL_LL
and QENC_INTRVL_UL to the encoder ranges that bracket the section of your stage
range that you wish to acquire. Interval mode can be used in conjunction with QENC_
AQ_DIR to acquire lines passing over the interval in the positive direction, the nega-
tive direction or both directions.
5.1.4 Re-Acquisition Prevention
Encoders are usually connected to mechanical systems which do not always move
smoothly. Because of these imperfections, there can be “jitter” in the quadrature
encoder signal. This jitter is not an electrical imperfection, but represent the reality of
the mechanical system vibrating, jumping, bouncing, etc. If these imperfections occur
during the period of time where lines are being acquired, the image will be distorted.
Lines on the object can be acquired more than once as the stage jitters. To prevent re-
acquisition of lines, a circuit has been added to the quadrature encoder system that
can prevent any line from being acquired more than once. To enable this mode, set
QENC_NO_REAQ = 1.
5.1.5 Scan Step Mode
The encoder can also be used to trigger acquisition of full frames from an area scan
camera. The idea is that every N lines, a trigger is issued to the board, which causes
acquisition of a frame. This can be used, for example, with a linear stage, where an
image is needed in steps across the range of the stage. This mode is enable by set-
ting SCAN_STEP_TRIG = 1, and programming SCAN_STEP to the number of encoder
counts per trigger.
5.1.6 Combining Modes
All of the modes above can be combined to support complicated encoder require-
ments. For example, the board can be programmed to acquire an interval in the posi-
tive direction only, with no lines being reacquired. Many combinations are possible.
5.1.7 Control Registers
Starting with Section 5.3 all of the registers needed to control the qudrature encoder
system are explained.