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132 Operation Theory

4.7 Position compare and Latch

The card provides position comparison functions on axes 0 and 1,

and position latching functions on axes 2 and 3. The comparison

function is used to output a trigger pulse when the counter reaches

a preset value set by the user. CMP1 (axis 0) and CMP2 (axis 1)

are used as a comparison trigger. The latch function is used to

capture values on all 4 counters (refer to section 4.4) at the instant

the latch signal is activated. LTC3 (axis 2) and LTC4 (axis 3) are

used to receive latch pulses.

4.7.1 Comparators of the 8164

There are 5 comparators for each axis of the card. Each compara-

tor has its unique functionality. Below is a table for comparison:

Note: Only comparator 5 has the ability to trigger an output pulse

via the CMP pin.

Comparators 1 and 2 are used for soft limits. Refer to section 4.9.

Comparator 3 is used to compare with the position error counter. It

is useful for detecting if a stepping motor has lost any pulses. To

enable/disable the step-losing detection, or set the allowable toler-

ance use _8164_set_error_counter_check()

The 8164 will generate an interrupt if step-losing is enabled and

has occurred.

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Adlink PCI-8164 Manual do Utilizador Página 144