Gemini 4100 Instruction Manual page 12

CODE 43 - INPUTS 1 & 2 RESPONSE MODES [Cont'd]
[43 2] COUNT WITH UP/DOWN CONTROL - In this mode, count direction
can be controlled by the second input. Input 1 serves as the count and rate input
and Input 2 serves as the direction control signal input. When Input 2 is at a
high level, the counter will count up. When Input 2 is at a low level, the counter
will count down. The rate is not affected by the directional control Input 2.
[43 3] TWO INPUT ANTI-COINCIDENCE ADD/SUBTRACT - This mode
effectively separates count pulses which may simultaneously appear at the
two inputs. The Gemini unit processes the count pulses into a string of
time-separated pulses, so the internal counter will not lose any count pulses.
Input 1 serves as the add and rate input (count increments) and Input 2 serves
as the subtract input (count decrements).
[43 4] SEPARATE INPUT - In this mode, the two functions, Counter (B) and
Rate (A) are independently controlled by the inputs. Input 1 serves as the Rate
(A) input and Input 2 serves as the Counter (B) input.
[43 5] QUADRATURE COUNTING - Quadrature counting modes are
primarily used in positioning and anti-jitter applications. The reason this mode
works is due to the manner in which two pickups are positioned relative to
each other. The signal on Input 2 is a pulse train signal shifted 90° away from
the Input 1 signal. These two signals are processed by the Gemini as follows:
Input 1 serves as the count and rate input, while Input 2 serves as the
quadrature input. For quadrature with single edge counting, the counter will
count in a positive direction when Input 1 is a negative going edge and Input 2
is at a low level. The counter will count in a negative direction when Input 1 is
a positive going edge and Input 2 is at a low level. All transitions on Input 1 are
ignored when Input 2 is at a high level. These logic rules provide the basis for
anti-jitter operation which will prevent false counts from occurring due to
back-lash, vibration, chatter, etc.
When two edge counting is used, the quadrature mode works the same as with
single edge counting when Input 2 is low. But when Input 2 is at a high level,
counts at Input 1 are no longer ignored. Instead the logic rules for Input 1 are
complemented, allowing both edges of Input 1 to be counted. This doubles the
effective resolution of the encoded input. The rate indicator will only use the
falling edge of the Input 1 signal, due to the method of rate indication used.
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[43 6] QUADRATURE TIMES 4 - This mode takes the quadrature mode, with
two edge counting, one step further. In quadrature times 4, both Input 1 and
Input 2 serve as the count or quadrature input, depending on their state. In one
instance, Input 1 will serve as the count input and Input 2 will serve as the
quadrature input. In another instance, Input 1 will be the quadrature input and
Input 2 will be the count input. This enables each edge, positive and negative
going, of both inputs, 1 and 2, to be counted. This results in a resolution four
times greater than in the basic quadrature x1 mode. As in the other modes,
Input 1 is also used for the rate input. The rate indicator will only use the
falling edge of the Input 1 signal, due to the method of rate indication used.
CODE 44 - COUNTER (B) NUMBER OF COUNT EDGES
The counter of the Gemini can be programmed for either single or two edge
(x2) counting. The number of count edges cannot be set when the count mode is
programmed for quadrature x4 operation. The Gemini will ignore any attempt to
enter function command code 44 when set for quadrature x4.
[44 1] SINGLE EDGE COUNTING (x1) - The unit counts on the negative going
(falling) edge of the count input signal. The count mode descriptions describe
how each mode uses this method of edge counting.
[44 2] TWO EDGE COUNTING (x2) - This mode is used when doubling of the
count signal input is required. The unit counts on the positive going (rising)
edge of the count input signal, as well as, the negative going (falling) edge.