MPV991 Curtiss-Wright VME Bus Timer / Counter Board

The Curtiss-Wright / Pentland Systems MPV991 VME bus Timer/Counter Board is supplied on a single 6U Card and complies with VME bus specification Rev. C.1.

The MPV991 is based around two Am9513A System Timing Controllers (STCA and STCB) each of which provides 5 general purpose 16 bit Timer/Counters. These 10 counters may be individually programmed to count UP or DOWN in either BCD or BINARY.

In addition each counter may be programmed to select its input from either one of four internal frequency sources (based on the 4MHz clock frequency) or one of four external pins associated with each STC, and to select active HIGH or active LOW input polarity. Both hardware and software gating of each counter is available, and each gate input may control up to three of its associated counters simultaneously.

The counters can be individually programmed to provide a pulse or toggled output directed to the outside world via a software enabled tri-state buffer. Counter outputs are also applied to an AM9519A Universal Interrupt Controller (UIC) which may be enabled to interrupt the host CPU via the VME Priority Interrupt Bus.

The accumulated count for each counter may be read at any time without disturbing the counting process. Any combination of counters for a given STC may be concatenated to provide an effective counter length up to 80 bits.

Quadrature detector circuits associated with each STC accept SINE and COSINE outputs from measurement devices such as optical shaft encoders and produce CW and CCW pulses which may be applied to one of the counters in order to determine the current device position. Up to four such devices may be connected to a single MPV991.

Communication with the MPV991 is achieved via the two 37 way D Type connectors P3 and P4 on the front panel (P3 associated with STCA and P4 associated with STCB) or alternatively via the P2 connector on the backplane.

Two standard versions of the MPV991 exist. They differ in the Non VME Digital Input lines interface. An MPV991D has differential line receivers terminated by 100 Ω, 1/2W resistors. The base model MPV991 employs standard 74LS14 hex Schmidt trigger invertors to interface to the outside world. All other aspects of the boards are identical.

The MPV991D is recommended for connection to devices which may be remote or located in noisy environments. For best results, line to line termination impedance should be adjusted to match the cable impedance used.