PCI-QUAD04 Measurement Computing Quadrature Encoder Input Board

The Measurement Computing / ComputerBoards PCI-QUAD04 Quadrature Encoder Input Board 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 +/-; and +5 VDC and GND (optional power for +5 V encoders).

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 heart of the PCI-QUAD04 is the LSI Computer Systems, Inc., LS7266R1 24-bit Dual-Axis Quadrature Counter IC.

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.

The PCI-QUAD04 also includes an 82C59 Programmable Interrupt Controller which accepts the four Index inputs directly and the Carry/Borrow outputs from the LS7266 (counter overflow/underflow or count value match) to generate interrupts to the PC bus. The interrupt controller operates in Polled Mode and allows for masking and priority setting of the interrupt inputs.