User's Manual

PMAC2 PCI Lite Hardware Reference Manual – Preliminary Documentation
Hardware Setup 7
Resistor Pack Configuration
Termination Resistors
The PMAC2 PCI Lite 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 PMAC2 PCI Lite 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 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:
Input Pack Pack Size Input Pack Pack Size
Encoder 1 RP60 6-pin ADC 1 & 2 RP60 8-pin
Encoder 2 RP62 6-pin ADC 3 & 4 RP61 8-pin
Encoder 3 RP66 6-pin ADC 5 & 6 RP121 8-pin
Encoder 4 RP68 6-pin ADC 7 & 8 RP122 8-pin
Encoder 5 RP107 6-pin Fault 1 & 2 RP63 6-pin
Encoder 6 RP111 6-pin Fault 3 & 4 RP64 6-pin
Encoder 7 RP108 6-pin Fault 5 & 6 RP124 6-pin
Encoder 8 RP112 6-pin Fault 7 & 8 RP125 6-pin
SCLK12&34 RP52 6-pin SCLK56&78 RP113 6-pin
Pull-Up/Pull-Down Resistors
The differential input signal pairs to the PMAC2 PCI Lite 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 kohm pull-up resistor to +5V. This cannot
be changed.
The - inputs of each differential pair each have a hard-wired 2.2 kohm resistor to +5V; each has another
2.2 kohm 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 used 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 kohm resistors act as a single 1.1 kohm pull-up resistor, holding the line at +5V in the
absence of an external signal. This configuration is required if encoder-loss detection is desired; or if
complementary open-collector drivers are used. It is permissible for differential line-driver inputs even
without encoder loss detection.
If Pin 1 of the resistor pack (marked by a dot on the pack) matches Pin 1 of the socket (marked by a wide
white line on the front side of the board and a square solder pin on the back side of the board), 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.