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Other VME hardware

  Several other VME cards are used in the system including the Bancomm IRIG decoder, parallel I/O cards, IEEE-488 interface cards, and analog to digital converter cards. All the chassis used in the telescope have at least three slots open for future expansion.

The Bancomm BC-635 card is used in each chassis to receive and decode IRIG signals from the site timing center, and synchronize the chassis to the site clock.

The parallel digital interfaces are Motorola MVME-340 cards. These cards provide 48 bits of I/O and three timers. The cards have software written for them that allows the higher-level software to read and write bits on the card without having to program all the registers on the interface chips. The inputs and timers on these cards are used to generate interrupts for synchronizing the systems in the telescope; for example, the Tracking Local Oscillator (LO) can switch frequencies on the edge of a signal/reference (sig/ref) or calibrate (cal) signal.

The Mizar MZ-7500, a IEEE-488 controller/talker/listener, is used to control the IEEE-488 based instruments. This card provides 2 channels via a pair of TMS-9914 chips. These chips provide an interface that is largely software driven and is not particularly reliable in a multitasking environment. There is a plan underway to replace the 9914 chips with a newer chip, possibly the INES i9914 chips. The INES i9914 devices provide much of the IEEE-488 functions in hardware, thereby allowing better performance and reliability, and reducing the amount of code in the device drivers.

Three analog to digital converter cards from VME Microsystems International Corporation (VMIC) are used to provide monitoring of the 16 azimuth and 8 elevation drive servos. These cards have 64 channels of 16 bit differential analog input.

John Ford
Fri Mar 13 16:06:38 EST 1998