PMDX-132 User’s Manual
PCB Revision: PCB-466A
Document Revision: 1.0
Serial Numbers: 23410 and above
PMDX-132_Manual_10.doc
©2008 Practical Micro Design, Inc.
Page 12 of 24
17 April 2008
All Rights Reserved
3.5.2 E-Stop Input
The
E-Stop
input provides an interface for external “emergency stop” circuits (see Figure 8 on page 11).
This signal is “active high”, such that a logic “high” tells the system to stop, and a logic low means “all is
OK”. The
E-Stop
input has a 2.2 Kohm pull-up resistor so that the default condition is “E-Stop”.
The
E-Stop
input should be connected to an external “normally closed” switch (or group of switches all
wired in series). The external switch(es) should be wired between the
E-Stop
pin and ground, such that
the switch contacts open to signal an emergency stop condition. If this input is not used, it must be
jumpered to ground. The PMDX-132 provides a 2.2K ohm pull-up resistor on the
E-Stop
input. This
means that the external emergency stop circuit must be capable of sinking 2.7 mA of current when the
switch contacts are “closed”.
The
E-Stop
,
Fault
and
Motor Disable
inputs are combined (logic “OR”) to drive pin 10 on the PC’s parallel
port and to enable or disable the data bus and control output buffers.
NOTE –
The
E-Stop
signal
must
be grounded (or driven low) in order for the data bus and
control output buffers to be enabled, and for the pin 10 status signal to the PC
parallel port to go low.
When any or all of the
E-Stop
(active high),
Fault
(active low),
Motor Disable
(active low) inputs, or any of
the Gecko driver’s “error” outputs are asserted, the following actions take place:
•
The ACK bit (corresponds to pin 10) in the PC’s status register reads as a “1” (to indicate “E-Stop”)
•
The LED labeled “Outputs Enabled” (reference designator DS12, along the right-hand edge of the
board) is “off”
•
The
Fault
daisy-chain output on J5 is tri-stated with a weak (10K ohm) pull-down
•
The control outputs are tri-stated with a weak (10K ohm) pull-down
•
The relays are de-energized
•
The data bus outputs to the Gecko stepper drivers are tri-stated
3.5.3 Motor Disable Input
The Motor Disable input allows external circuitry to place the stepper motors into a “minimum torque”
condition. It does so by overriding the “current set” resistors and setting the motor current to “near”
zero. The amount of holding torque while “disabled” will depend on the motors used. This “disable”
function allows for manual operation of the motors by removing most, but not all of the motor torque.
An emergency stop condition is also signaled when Motor Disable occurs. This disables the step and
direction outputs and any controls (such as spindle power) normally turned on by the outputs. Any
controls that need to operate while in “manual” mode must have a manual override.
This input is active low and has a 2.2 Kohm pull-up resistor so that it may be left unconnected when not
used. To disable the motor drivers, drive this input to ground via open-collector or TTL style drivers or
mechanical switches.
NOTE –
The Motor Disable signal
must
be either driven high (+5V) or allowed to float in
order for the motor driver’s step inputs to be enabled and the pin 10 status signal to
the PC parallel port to go low (signaling “OK”). If you do not have any motor disable
circuitry, leave this input unconnected.
3.6
Charge Pump (watchdog)
The charge pump circuit (also called a watchdog circuit) is designed to disable the PMDX-132 and all
stepper motor drivers when the software running on the PC stops working properly. The charge pump
also keeps the PMDX-132 disabled while the PC starts up (i.e. all outputs are disabled until the PC boots
