Hardware Reference Manual
Hardware Setup
7
Differential Encoders
Differential encoder signals (pin 2 to 3) can enhance noise immunity by providing common-mode noise
rejection. Modern design standards virtually mandate their use for industrial systems, especially in the
presence of PWM power amplifiers, which generate a great deal of electromagnetic interference.
Connect pin 1 to 2 to tie differential line to +2.5V
• Tie to +2.5V when no connection
• Tie to +2.5V for single-ended encoders
Connect pin 2 to 3 to tie differential line to +5V
• Don’t care for differential line driver encoders
• Tie to +5V for complementary open-collector encoders (obsolete)
Reserved Configuration Jumpers
E0: Reserved for future use
Resistor Packs Configuration (older rev boards without E20-23)
Differential or Single-Ended Encoder Selection
The differential input signal pairs to the PMAC have user-configurable pull-up/pull-down resistor
networks to permit the acceptance of either single-ended or differential signals in one setting, or the
detecting loss of differential signals in another setting.
The ‘+’ inputs of each differential pair each have a hard-wired 1 k
Ω
pull-up resistor to +5V. This cannot
be changed.
The ‘-‘ inputs of each differential pair each have a hard-wired 2.2 k
Ω
resistor to +5V; each also has
another 2.2 k
Ω
resistor as part of a socketed resistor pack that can be configured as a pull-up resistor to
+5V, or a pull-down resistor to GND.
If this socketed resistor is configured as a pull-down resistor (the default configuration), the combination
of pull-up and pull-down resistors on this line acts as a voltage divider, holding the line at +2.5V in the
absence of an external signal. This configuration is required for single-ended inputs using the ‘+’ lines
alone; it is desirable for unconnected inputs to prevent the pick-up of spurious noise; it is permissible for
differential line-driver inputs.
If this socketed resistor is configured as a pull-up resistor (by reversing the SIP pack in the socket), the
two parallel 2.2 k
Ω
resistors act as a single 1.1 k
Ω
pull-up resistor, holding the line at +5V in the absence
of an external signal. This configuration is required if complementary open-collector drivers are used; it
is permissible for differential line-driver inputs.
If Pin 1 of the resistor pack, marked by a dot on the pack, matches Pin 1 of the socket, labeled by a white
square, then the pack is configured as a bank of pull-down resistors. If the pack is reversed in the socket,
it is configured as a bank of pull-up resistors. The following table lists the pull-up/pull-down resistor
pack for each input device:
Device
Resistor Pack
Pack Size
Encoder 1
RP30
6-pin
Encoder 2
RP31
6-pin
Encoder 3
RP36
6-pin
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
