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ADVANCED MICRO SYSTEMS, INC. SMC-27X2 SOFTWARE
38
Function Type NV Bytes
Find Home Immediate, Program 3
Command
F
Mnemonic
(Name) F (n, d)
Data 1
SPS (40-36,000)
Data 2
Direction (0,1)
Result
None
F (Find Home)
The special Home algorithm is intended to eliminate mechanical hysteresis typically found in many switches,
encoders and is generally present in the form of system mechanical backlash.
The SMC-27X2 microprocessor implements an intelligent homing algorithm whereby home is always
approached from the same direction based on the initial logic state of the Home switch and the value (0 or 1)
assigned to the “d” direction byte.
Normally Open Home Switch
The Find Home step velocity, using a normally open Home switch (actuation from logic high to low) is
programmable over the entire slew velocity available, from 40-36,000 SPS. Once the Home switch is
encountered the system inertia typically overshoots the exact switch transition point so that the controller
changes the direction signal and shifts the step speed down to the (I) initial parameter velocity. This
direction reversal and speed reduction continues until the exact Home switch actuation point is reached and
the Homing function is complete.
Normally Closed Home Switch
The Find Home step velocity, using a normally closed Home switch (actuation from logic low to high) will
always be the (I) initial velocity parameter setting. Once the Home switch is actuated all motion ceases and
the Homing function is complete. The following table illustrates the possible combinations of switch motion:
Home Switch
“d”
Parameter
Direction of Motion
Normally Open (High to Low) 0 Negative
Normally Closed (Low to High) 0 Positive
Normally Open (High to Low) 1 Positive
Normally Closed (Low to High) 1 Negative
This command may be implemented within a program. Following, is an example:
P 0 Enter program mode.
F 1000 1 Find the home switch in the “1” direction at a step rate of 1000 SPS.
P Exit program mode.
Function Type NV Bytes
Execute Program Immediate, Program 3
Command
G
Mnemonic
(Name) G (a, t)
Data 1
0-192, 256-2048
Data 2
Trace (0-1)
Result
None
G (Go)
The Go command is used to execute a user programmed sequence starting at location “a.” Most programs
will start at “0”, however, you may wish to start at another address. The address MUST begin at a stored
instruction address, i.e., “go to” data produces unpredictable results.