LAC-1 single axis controller manual

SMAC
LAC-1 Technical Reference Manual
1.2 Digital I/O Interface
The LAC-1 includes 8 channels of HCT TTL general purpose digital input and 8 channels
of HCT TTL general purpose digital output. Additionally, there are four channels of TTL dedicated
digital input. The general purpose I/O are buffered with 74HCT541. An expansion interface allows
for optional expansion of I/O to 64 channels.
1.2.1 Dedicated Digital Inputs
The LAC-1Õs dedicated digital inputs are Limit+, Limit-, Home and Fault. Figure 1. LAC-1
Dedicated Input. illustrates one of these inputs. All of these inputs are active low and have 2.7K
ohm pull up resistors. To activate one of these inputs, the user need only connect that input to the
controllerÕs ground.
The Limit inputs are intended for signaling the LAC-1 that an axis has reached itÕs end of
travel. When such an event occurs, the LAC-1 can ignore the event or stop the servo in some
controlled fashion. The Home input is for detecting some sort of "home position" sensor. This can
be used with the encoder Index input to implement a very accurate homing method. A typical use
for the Fault input is for an external device to signal a fault condition such as motor/actuator overtemperature.
Note: The external Fault input is tied to the internal over-temperature signal from the onboard
driver. When a fault condition occurs, that is either the internal over-temperature signal or
external Fault signal go active, the 16-bit internal variable FCNT (see Internal Variables)
begins to increment at a rate of once per millisecond. If the fault condition clears, then the
FCNT variable is also cleared. If the fault condition remains present long enough for the
FCNT variable to count up to the value assigned to the FCMP variable, then the Fault bit in
the status word will be set and the servo will be disabled (assuming the Fault interrupt has not
been enabled). The default value for FCMP is 10000 which will give a 10 second delay
before causing the Fault bit to be set.
Figure 1. LAC-1 Dedicated Input.
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