2.10.1.8 - Quadrature Input (Mode 8) [UE9 Datasheet]

Requires 2 timer channels used in adjacent pairs (0/1, 2/3, or 4/5). Even timers will be quadrature channel A, and odd timers will be quadrature channel B. The UE9 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 even and odd 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.

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

Z-phase support requires Control Firmware 2.11 or later.

2's Complement

Other timer modes return unsigned values, but this timer mode is
unique in that it returns a signed value from -2147483648 to
+2147483647.  That is, a 32-bit 2's complementvalue.  When you do a timer value read and get back a single float from
the UD driver, the math is already done and you get back a value from
-2147483648.0 to +2147483647.0, but when using the special channels
20x/23x/224 you get the LSW and MSW separately and have to do the math
yourself.  Search for 2's complement math for your particular
programming language.

In a language such as C++, you start by doing using unsigned 32-bit
variables & constants to compute Value = (MSW * 65536) + LSW.  Then
simply cast Value to a signed 32-bit integer.

In a language such as Java that does not support unsigned integers,
do everything with signed 64-bit variables & constants.  First
calculate Value = (MSW * 65536) + LSW.  If Value < 2147483648, you
are done.  If Value >= 2147483648, do ActualValue = -1 * (4294967296 -
Value).