2.9.1.8 - Quadrature Input (Mode 8)

Requires both timers, where Timer0 will be quadrature channel A, and Timer1 will be quadrature channel B. Timer#Value passed has no effect. The U3 does 4x quadrature counting, and returns the current count as a signed 32-bit integer (2’s complement). The same current count is returned on both timer value parameters.

Writing a value of zero to either or both timers performs a reset of both. After reset, a read of either timer value will return zero until a new quadrature count is detected. If a timer is reset and read in the same function call, the read returns the value just before the reset.

4X Counting

Quadrature mode uses the very common 4X counting method, which provides the highest resolution possible.  That means you get a count for every edge (rising & falling) on both phases (A & B).  Thus if you have an encoder that provides 32 PPR, and you rotate that encoder forward 1 turn, the timer Value register will be incremented by +128 counts.

Z-phase support

Quadrature mode supports Z-Phase. When enabled this feature will set the count to zero when the specified IO line sees a logic high.

Z-phase is controlled by the value written to the timer during initialization. To enable z-phase support set bit 15 to 1 and set bits 0 through 4 to the DIO number that Z is connected to. EG: for a Z-line on EIO3 set the timer value to 0x800B or 32779. This value should be sent to both the A and B timers. When enabled this feature will set the count to zero when the specified IO line sees a logic high.

Note that the LabJack will only check Z when it sees an edge on A or B.

Z-phase support requires Firmware 1.30 or later.