ADLINK Technology NuDAQ PCI-9222, Руководство пользователя

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60 Operation Theory
X4 Encoder Mode
This mode is similar to X1 Encoder Mode, except that the
amount of counter value increases or decreases by four. Refer
to Figure 4-35.
Figure 4-35: X4 Encoder Mode
Phase Z
Each encoder mode may use a third phase, phase Z, that is
also frequently used for the index phase. You may decide if the
counter needs to be reloaded a specified value when phase Z
is at a logic high level with phase A and B at a specific logic
condition.
You must ensure that the logic level of phase Z is high during
at least a portion of the phase you specify for reload when you
use phase Z. Otherwise, the counter does not reload.
In Figure 4-36, the reload phase is when the logic level of
phase A is high, phase B is low, and phase Z is high in X1
Encoder Mode. In addition, reloading takes higher priority than
increment or decrement of counter value. The reload occurs
within one maximum CLK period after the reload phase
becomes true. After the counter value is reloaded, the counter
continues to count as before.