MVD analog spy channels

Multiplexed readout of analog spy channels

Last update: 7 Nov 97 - HvH

Each MCM has 2 spy channels, one at the preamp output and one at the AMU output, for a total of 2x42 analog channels per MVD motherboard (of which there ar 4). We propose to use Analog Devices ADG46, which are analog multiplexers. They take 16 inputs, and connect one of these to the output, depending on the value of 4 switch bits (a0-a3), and on the level of the enable line.

Shown below is the proposed arrangement for 1 motherboard. There are 3 pairs of multiplexers (2 pairs are drawn), each pair sharing an enable line, since we lways want to look at the preamp and AMU signals from the same MCM. Thus an MCM is selected by setting the appropriate levels on enable1,2,3 and a0-a3.

From each mother board there are 7 digital lines going in and 2 analog lines coming out. On the Black-Box end, a small program in the VME crate processor will read and write the 7 lines via a digital I/O module, much in the way we now have the XIL program load the Xilinx chips on the mother board in the clean tent.

As shown on the preceding page, the analog signals are put onto Glink and sent to the control room, whre they are un-converted.

One further option is to multiplex the signals in the balack box down from 4 pairs to 1 pair, so that only 2 Glinks go to the control room, one preamp signal and one AMU signal.

QUESTIONS TO BE RESOLVED: 1) The VME CPU runs the C program and ends up with the values in its memory, or writes them to disk. How do we get the numbers from there into EPICS? Is this done with a Virtual Device?

2) Can we have EPICS fire up this serial program?

WHAT CAN BE DONE RIGHT NOW: Obtain a multiplexer, and use the existing hardware in the clean tent (HP, VME, CAMAC, I/O module) to write the control program and verify this scheme.

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Hubert van Hecke