The 4I30 is a stackable PC/104 card with four 32 bit up/down counters with quadrature count inputs and per channel index inputs.  The 4I30 is intended for robotic, motor control, measurement, and instrumentation applications.  The 4I30 has selectable TTL or RS-422 levels on its quadrature and index inputs.  TTL or RS-422 operation is jumper selectable in groups of two channels.  The TTL inputs have pullup resistors and RC / Schmitt filtering.  The differential RS-422 inputs are suited for longer cable lengths and have optional termination.  Each time a logic transition occurs at one of the quadrature inputs, the count is incremented or decremented, providing a resolution of four times the line count of the encoder used.  The 4I30 counters may cleared individually, or all counters may be cleared simultaneously. Each counter has a separate programmable count enable/disable with external index input.  The 4I30 can be programmed so that the count is synchronized with the external index signal.  Index signal polarity is jumper selectable.  Maximum count rate of the 4I30 is 1.5 million/second.  Count range is -2,147,483,648 to +2,147,483,647 or 0 to 4,294,967,295.  One counter may be configured to provide a timing reference for velocity calculations instead of quadrature input.  This timing reference is a 32 bit up counter running at 500 KHz +- .01%.