Front-End Electronics (FEE)

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Front-End Electronics (FEE)
	Maintenance
	Last modified: 14:10 Friday 01-Oct-1999

Grounding sheets: The aluminum FEE-cooling manifold is not necessarily, by itself, an adequate, low-impedance, common ground for the FEE cards - especially because the tubes are epoxied together and are not necessarily even connected electrically. Thin, gold-plated, copper sheets lay over the manifold surface, considerably reducing the electronic noise.
FEE cooling and interlock: The FEE power supplies are intended to be used with a water flow interlock that assures a flow of 3 liters/minute, or more, through the readout board manifolds; lower flow rates do not ensure that coolant flows through all tubes.
FEE cards: The 24x181 FEE cards to be mounted on the TPC are nominally interchangeable, although cards from older generations exist elsewhere. They are powered through the readout boards. The FEE card locations within a sector have been assigned ID numbers, and these are etched into the pad plane.
Readout boards (RDO's): References and general information
Each readout board has as many as nine sections. Each section is equipped with a Xilinx programmable logic chip, independent voltage regulators and a pair of connectors and cables, supporting up to four FEE cards. No more than 36 FEE cards connect to a single RDO.
FEE card pedestals and pedestal RMS are very sensitive to readout board grounding conditions. Lower impedance connections (i.e., grounding braid) to the sector tend to reduce RMS. A twisted-pair trigger cable supplies a bused 4-bit trigger word to each attached readout board. The connectors are unkeyed, relying on the user to align "Pin 1's" of the cable plug and RDO connector; on each, "Pin 1" is marked by a small triangle molded into the side of the connector. The RDO end of the cable must be terminated with (eight?) 100--120 ohm resistors. Inner and outer sectors are usually supplied with independent cables.
The following hex trigger words are defined for the readout boards in Trigger/Clock Distribution Tree, (Req. Doc., V1.2, February 29, 1996), by V. Lindenstruth et al.:
- 0: No trigger; following trigger token is 0
- 1: Clear; clears redundancy counters
- 2: Master reset; general reset of whole FEE logic
- 3: Reserved
- 4: Trigger 0; physics readout (normal trigger)
- 5: Reserved; executed as Trigger 0
- 6: Reserved; executed as Trigger 0
- 7: Executed as Trigger 0, but copy event also to local buffer
- 8: Charge-injection pulser
- 9: Laser trigger
- A: Ground-plane pulser
- B: Buffered readout; reproduce event stored by Trigger 3
- C: Config; housekeeping or geometry event
- D: Abort; abort and clear active event
- E: L1 accept; Level 1 accepted the event identified by token
- F: L2 accept; Level 2 accepted the event identified by token
Slow controls can monitor a number of readout board parameters. This includes two thermocouples on leads that can plug into the RDO. The slow controls interface is attached through a flat, narrow ribbon cable. The RDO end of this cable must also be terminated with (six?) 100--120 ohm resistors. MiniDAQ per se can operate without these connections.
Each readout board is also equipped with a modem interface, and their address space can be accessed via this.
Separate floating magneto-resonance power supplies provide +/- 8 VDC to each RDO. The + and - current draws are similar, making the ground return current small. (On an early prototype with a lower quality power connector, the potential developed across a bad ground connection may be too low to clear the oxide layer.)
Data is sent to DAQ via a 50- or 62.5-um multi-mode fiber. This link is strictly one way.
RDO ID convention: Each of the TPC's 144 RDO's is assigned a unique 8-bit ID of the form SSSSS.RRR --- where SSSSS is the Sector ID (1-24) and RRR is the RDO location (1-6) on the sector, as per the standard convention. Any ID's not matching these criteria are illegal. For testing flexibility, the RDO ID is currently set by an 8-bit DIP switch on each RDO.
Note: the RDO ID is loaded only as the RDO is powered up; changing the DIP-switch settings does not change the RDO ID until it is power-cycled. If the ID is not correct, the data will be corrupted, unanalyzed and/or incorrectly analyzed.
FEE-to-readout board cabling: A single sector cabling scheme is defined and should always be used, except for debugging.
FEE power supplies and cables: Each readout board is powered by a rack-mounted supply through one six-wire cable. The plug is polarized and locking. (A pneumatic crimper is required to replace one.) Readout board power is switched individually with a three-position, locking switch; pull the switch out slightly to change positions. The up position is "on," the middle position is "off," and the down position puts them under remote control.
Trigger cable(s): The trigger cable must be installed with a bit of care. The connectors on the cable are not mechanically keyed, but have "Pin 1" marked by a small triangle molded into the side. This must be aligned with the similarly marked "Pin 1" on the trigger card and readout boards. The markings on the trigger-card connectors faces the VME crate, making them almost impossible to see, but it suffices to know that the marking on the cable connector also has to face the crate. The end opposite the trigger card must be terminated with 100--120-ohm resistors.
Optical fibers: The multi-mode optical fibers are bundled in groups of eight. While not extremely fragile, several have been damaged; in the present bundle, #3 and #7 are dead and marked with red tape.