Measurement Computing PCI-QUAD04 - Manual (Page 6)

6
Chapter 1
Introducing the PCI-QUAD04
Overview: PCI-QUAD04 features
The PCI-QUAD04 is a PCI plug-in board that provides inputs and decoding for up to four incremental
quadrature encoders. The PCI-QUAD04 can also be used as a high speed pulse counter for general counting
applications.
Incremental quadrature encoders are used to provide feedback signals from motors, that is, to count rotations
and convert the physical movement into a series of electrical signals. These signals are sent to the computer
which then decides whether or not to trigger signals that control the motor’s movement and what those control
signals should be. The PCI-QUAD04 is the link between up to four incremental quadrature encoders and the
computer.
The PCI-QUAD04 is a plug-in board that uses one PCI slot and a 37 pin D-type connector for up to four
channels. Each incremental quadrature encoder connects to an input channel on the board through a DB37
female connector on the board’s rear panel. Channels 1 through 4 connect to the DB37 connector on the rear
panel bracket.
For each channel, the signals provided at the DB37 connectors are:
 Phase A+, A-
 Phase B+, B-
 Index ±
 +5 VDC and GND (optional power for +5 V encoders)
Pinout diagrams are shown on page 11.
The PCI-QUAD04 provides inputs for three basic signals, Phase A, Phase B, and Index. Phase A and Phase B
are generated at a 90° phase shift with respect to each other. Using these signals, a computer can determine
system position (counts), velocity, (counts per second), and direction of rotation.
The Index signal is used to establish an absolute reference position within one count of the encoder rotation
(360°). Therefore, the Index signal is often used to reset or preset the position counter, particularly upon system
startup when the incremental encoder cannot determine the starting position of the motor. The Index signal can
also be used to generate an interrupt signal to the computer.
The Phase A, Phase B, and Index inputs are jumper-selectable for differential or single-ended input mode.
These signals, after being routed through differential receivers, offer various paths to the LS7266 inputs through
the FPGA. The inputs are register-programmable for the following:
 Individual incremental encoder inputs to allow up to four channels
 Cascadable counters to allow non-quadrature counting up to 96-bits
 Routing the Index input to either the Load Counter/Load Latch input or the Reset Counter/Gate input with
quarter cycle and half cycle signals
 Routing the Compare or Carry/Borrow output signals to the 8259 Interrupt controller
The heart of the PCI-QUAD04 is the LSI Computer Systems, Inc., LS7266R1 24-bit Dual-Axis Quadrature
Counter IC. This component contains:
 Two 24-bit counters with associated 24-bit preset and 24-bit output latch registers
 Integrated digital filtering with 8-bit counter prescalers
 Programmable index functionality and programmable count modes including non-quadrature modes
The PCI-QUAD04 can operate as a high-speed pulse and general purpose counter, cascadable to 96-bits. The
24-bit counters can count either in binary or BCD through register programming.