Delta Tau GEO BRICK LV User Manual
Turbo PMAC User Manual
50
Setting Up Feedback and Master Position Sensors
Note:
When using single-ended TTL-level digital encoders, the complementary line input
should be left open, not grounded or tied high; this is required for PMAC's
differential line receivers to work properly.
should be left open, not grounded or tied high; this is required for PMAC's
differential line receivers to work properly.
It is possible to pull the complementary line as well to 5V. On most Turbo PMAC boards, this is done by
changing the setting of a 3-point jumper for the encoder channel. On Turbo PMAC2 boards and systems
(including UMAC), this is done by reversing a SIP resistor pack in its socket.
changing the setting of a 3-point jumper for the encoder channel. On Turbo PMAC2 boards and systems
(including UMAC), this is done by reversing a SIP resistor pack in its socket.
PMAC Encoder Input Circuitry
y
Connect pin 1 to 2 to tie differential line to +2.5V
y
Connect pin 2 to 3 to tie differential line to +5V (Reversible socketed SIP on PMAC2)
y
Tie to +2.5V when no connection
y
Tie to +2.5V for single-ended encoders
y
Do not care for differential line driver encoders
y
Tie to +5V for complementary open-collector encoders (obsolete)
y
Tie to +5V to support external XOR loss of encoder circuitry
Encoder-Loss Detection Circuitry
The main reason to pull up the complementary line is to enable the encoder-loss detection circuitry that is
present on many Turbo PMAC and interface boards. This circuitry uses exclusive-or (XOR) logic that
requires that the signals of each pair be in opposite logical states for it to consider the encoder present. If
the encoder fails or the cable becomes disconnected, both inputs of the pair pull high to a logical 1, and
the circuitry indicates encoder loss. Check the appropriate hardware reference manual to see if your
device has encoder-loss detection and how it is implemented.
present on many Turbo PMAC and interface boards. This circuitry uses exclusive-or (XOR) logic that
requires that the signals of each pair be in opposite logical states for it to consider the encoder present. If
the encoder fails or the cable becomes disconnected, both inputs of the pair pull high to a logical 1, and
the circuitry indicates encoder loss. Check the appropriate hardware reference manual to see if your
device has encoder-loss detection and how it is implemented.
Termination Resistors
When driving the encoder signals over a long cable (10 meters or more), it may be desirable to add
termination resistors between the main and complementary lines to reduce the ringing on transitions.
PMAC provides sockets for resistor packs for this purpose. The optimum value of the termination
resistor is system dependent; ideally matching the characteristic impedance of the cable, but 330 ohms is
a good starting point.
termination resistors between the main and complementary lines to reduce the ringing on transitions.
PMAC provides sockets for resistor packs for this purpose. The optimum value of the termination
resistor is system dependent; ideally matching the characteristic impedance of the cable, but 330 ohms is
a good starting point.