ADLINK PCI-8124-C - Manual (Page 38)

28 Operation Theory
4.1.1 Encoder Channel
The PCI-8124-C has four 32-bit binary up/down counters to keep
the present feedback position from each encoder channel. The
counter counts signal inputs from the EA and EB pins. The counter
source could be assigned to internal timer.
It accepts 3 types of pulse inputs: (1). Single pulse mode (OUT/
DIR) (2) Dual pulse mode (CW/CCW) (3) 90° phase shifted sig-
nals (AB phase mode). 90° phase shifted signals maybe multiplied
by a factor of 1, 2 or 4. The 4xAB phase mode is the most com-
monly used in incremental encoder device. For example, if a
rotary encoder has 2000 pulses per phase (A or B phase), then
the value read from the counter will be 8000 pulses per turn or –
8000 pulses per turn depending on its rotating direction. The three
options will be explained as follows.
Single Pulse Mode (OUT/DIR Mode)
In this mode, EA is dedicated to the count the pulses and EB is to
represent the direction. Simply put, we call it as PULSE/DIR
mode. The DIR signal represents direction as positive (+) or nega-
tive (-). User can decide the normal high or normal low for those
two channels according to users’ devices. For example, we set
these two input channel as normal high. The EA can count the
pulse input when the signal level changes from high to low. EB will
see the high level as positive direction unless the level changes to
low level. The waveform is as follows.