Oops! Powering the RS485 transceivers

Revision 0 of the cryoelectronics boards do not correctly power the RS485 transceiverse (U43 and U44, just above the S/N label.)

The easiest way to re-attach power to these parts is shown in Fig. 1. Connect the +3V3 end of C165 to pin 8 of U44.

Fig. 1: Rework

Timestamp Formatting

It would be nice to dump the timestamp firmware from the DfMUX directly into the cryo board design, but it's not feasible. See FX12Usage for details. Instead, we're hoping to replace two (large) timestamp decoders and a multiplexing block with a simpler decoder that handles both timestamps.

This page is basically a feasibility study and logbook for such a beast.

IRIG-B Formatting

According to an e-mail from John Joseph,

I decoded the IRIG-B straight BCD format (no modulation). Look at pg 6-7 (Figure 6-2) for the page that I used for the standard. I decoded the bit stream with a UART type decoder that measured the pulse width of each bit in the data stream. Most likely there are better ways to do this, but this turned out to be the simplest for me.

The linked document is here.

Time Link Decoder

The EBEX time system is described here. The cryo board receives a 40-bit signal, plus four bits each of start and end marker. This signal is Manchester-encoded.

There are a number of discrepancies between this document and the timestamp capture sent to me by Francois:

• the symbol rate is 2 MBPS, suggesting a minimum sampling rate of 4 MBPS (since the Manchester portion of the signal contains two transitions per symbol.)

Timestamp Peripheral

The timestamp peripheral consists of three main elements: a sampling synchronizer, symbol detectors, and an output buffer. These elements are configured via a memory-mapped set of registers described below.

Sampling Synchronizer

Symbol Detectors

Output Buffer

Register Map

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This topic: CryoElectronics > WebHome > TimestampPeripheral Topic revision: r3 - 2009-10-29 - GraemeSmecher

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