User's Manual

Turbo PMAC PCI Lite
8 Hardware Setup
Resistor Pack Configuration: Flag and Digital Inputs Voltage Selection
The PMAC is provided with 6-pin sockets for SIP resistor packs for the input flag sets. Each PMAC is
shipped with no resistor packs installed. If the flag or digital inputs circuits are in the 12V to 15V range,
no resistor pack should be installed in these sockets. For flags or digital inputs at 5V levels, quad 1k SIP
resistor packs (1KSIP6C) should be installed in these sockets. The following table lists the voltage
selection resistor pack sockets for each input device:
Device
Resistor Pack
Flags 1
RP77
Flags 2
RP83
Flags 3
RP89
Flags 4
RP94
Resistor Pack Configuration: Termination Resistors
The PMAC provides sockets for termination resistors on differential input pairs coming into the board.
As shipped, there are no resistor packs in these sockets. If these signals are brought long distances into
the PMAC board and ringing at signal transitions is a problem, SIP resistor packs may be mounted in
these sockets to reduce or eliminate the ringing.
All termination resistor packs are the types that have independent resistors (no common connection) with
each resistor using two adjacent pins. The following table shows which packs are used to terminate each
input device:
Device
Resistor Pack
Pack Size
Encoder 1
RP61
6-pin
Encoder 2
RP63
6-pin
Encoder 3
RP67
6-pin
Encoder 4
RP69
6-pin
Resistor Pack Configuration: 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
detection of lost differential signals in another setting.
The ‘+’ inputs of each differential pair each have a hard-wired 1 k pull-up resistor to +5V. This cannot
be changed.
The ‘-‘ inputs of each differential pair each have a hard-wired 2.2 k resistor to +5V. Each also has
another 2.2 k 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.