Red Lion GEMINI 2 - Manual (Page 10)

PROGRAMMING INSTRUCTIONS FOR THE COUNTER VERSION OF THE GEMINI
The first part of this section provides detailed description of the function
command codes for counting modes, reset modes, output terminations, etc. Then,
using an actual application example, the programming instructions for a counter
version will be “walked through”, to give the user a full understanding of the
Gemini programming procedure. The descriptions below give the function
command code first, followed by the individual mode identifier. The Function
Command Code Summary in the appendix lists all codes. (Only commands and
modes pertaining to the counter will be discussed in this section.)
CODE 41 - UNIT PERSONALITY
Two basic personalities are available for the Gemini. They are the counter
mode and the rate indicator mode.
[41 1] COUNTER - Setting this mode selects the unit to function as a counter.
This is the basic personality mode and must be programmed before any
other modes are set. (This command forces default mode values in certain
command codes.)
CODE 43 - INPUTS A & B RESPONSE MODES
The Gemini has six different input response modes. They are: Count with
Inhibit; Count with Up/Down Control; Two-Input Anti-Coincidence Add;
Two-Input Anti-Coincidence Add/Subtract; Quadrature; and Quadrature X4.
[43 1] COUNT WITH INHIBIT - Input A in this case, serves as the count
input. Input B serves as the inhibit terminal. When Input B is low, count
signals appearing at A will be ignored. When Input B is at a high level,
negative going (falling) signals appearing at A will be counted.
[43 2] COUNT WITH UP/DOWN CONTROL - When in this mode, count
direction can be controlled by a second input. Input A serves as the count
input, and Input B serves as the direction control signal. When B is at a
high level, negative going transitions at A will cause the unit to count in
the positive direction. When Input B is at a low level, negative going
transitions at A will cause the counter to count in the negative direction.
[43 3] TWO (2) INPUT ANTI-COINCIDENCE ADD/SUBTRACT - This mode
effectively separates count pulses which may simultaneously appear at the
two inputs. The Gemini unit then processes the count pulses into a string of
time-separated pulses, so the internal counter will not lose any counts. Input
A serves as the add input, and Input B serves as the subtract input.
[43 4] TWO (2) INPUT ANTI-COINCIDENCE ADD - This mode functions
in the same manner as the Two Input Add/Subtract mode except both
Input A and Input B serve as “ADD” inputs.
[43 5] QUADRATURE COUNTING - Quadrature counting modes are
primarily used in positioning and anti-jitter applications. The reason this
mode is used is due to the manner in which two pickups are positioned
relative to each other. Input B is a pulse train signal shifted 90° away from
Input A. These two signals are processed by the Gemini as follows:
Input A serves as the count input, while Input B serves as the quadrature
input (B is the input shifted 90° away from A). For quadrature with single edge
counting, the counter will count in a positive direction when Input A is a
negative going edge and Input B is at a low level. The counter will count in a
negative direction when Input A is a positive going edge and Input B is at a
low level. All transitions on Input A are ignored when B 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 B is low. But when Input B is at a high
level, counts at Input A are no longer ignored. Instead the logic rules for A are
complemented, allowing both edges of A to be counted. This doubles the
effective resolution of the encoded input.
[43 6] QUADRATURE TIMES 4 - This mode takes the quadrature mode, with
two edge counting, one step further. In quadrature times 4, both Input A and
Input B serve as count or quadrature input, depending on their state. In one
instance, Input A will serve as the count input and Input B will serve as the
quadrature input. In another instance, Input A will be the quadrature input
and Input B will be the count input. This enables each edge, positive and
negative going, of each input, A and B, to be counted. This results in a
resolution four times greater than in the ordinary quadrature mode.
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