Some General Notes about Cables in the FW ----------------------------------------- D ***** Companies ***** First, a list of companies that make twist'n'flat style cable: AMP: 1-57709-7 3M: Belden: 9V Amphenol Spectra-Strip: 843-132 Alpha: 3586 ***** Lengths ***** Next, a few notes about what lengths of cable can be made. Using AMP as an example, twist'n'flat type cable is available with twist sections of 6", 12", 18" and 24" as standard choices. For these cables, the flat sections are 2" long, making the unit cell 8", 14", 20", and 26", respectively. Recall that we typically buy the 18" section cable. Let's ignore the 6" cable, as its ratio of twist to flat is not attractive. The 12" cable may have the same problem, so we'll only use it if we really need it. Typically, we cut the cable in the middle of the flat sections, to minimize waste. This gives a raw cable the length of which is just a multiple of the unit cell. The finished cable (with connectors installed) is about 1" shorter than the raw cable. But note that we could put the connector anywhere within about +/- 0.75" of the center of the flat section. By carefully positioning both connectors, we can make cables with lengths about +/- 1.5" around the nominal length. Here is a table of possible finished cable lengths: Number of Type of cable sections: 12" 18" 24" 1 11.5" - 14.5" 17.5" - 20.5" 23.5" - 26.5" 2 25.5" - 28.5" 37.5" - 40.5" 49.5" - 52.5" 3 39.5" - 42.5" 57.5" - 60.5" 75.5" - 78.5" 4 53.5" - 56.5" 77.5" - 80.5" 101.5" - 104.5" In practice, let's only consider three types of cables: minimal: nominal length - about 1.5" nominal: nominal length maximal: nominal length + about 1.5" Finally, note that a short cable (specifically a minimal length cable) can generally be replaced by a slightly longer (e.g. nominal length) cable if so desired. ***** Cables vs. Paddleboards ***** The Front Paddleboard, various flavors of Rear Paddleboard, and the Pass- Through Card were all designed to work cleanly in the "typical" situations, but there are issues to be dealt with. 1. TDM Paddleboard Chain The TDM Paddleboard Chain consists of a bussed component (Exposure Group type signals) and a radial component (Partial And-Or Fired type signals). The bussed signals are found on a Pass-Through that is on the low side (i.e. lower slot number) of the TDM Chain. Panduit "stacking" connectors are used to bus the bussed signals. If the connectors are inserted from the COMPONENT side of the Paddleboards, the chain looks like (from the top): BACKPLANE | | | [|--[|--[|-- Bit 0 DIR [|--[|--[|-- Bit 0 COM | | | There are three things to note about this: 1. the pins emerging from the SOLDER SIDE of the low end (lower slot number) end of the chain do not allow a rear paddleboard to be put behind the Exposure Group type Pass-Through. 2. Plugging a standard female mass termination connector onto these pins swaps either the ORDER or POLARITY of the signals injected into the chain. 3. Plugging a standard (i.e. internally "reversed", intended to make extension-type cables) MALE mass termination connector onto the RIGHTMOST (high-side) Panduit connector ALSO reverses either the ORDER or POLARITY. The solution is to use individual twisted-pair wires (with AMP crimp connectors) to make a wiring harness which plugs directly into the backplane behind the Pass-Through, and also plugs on to the pins emerging from the solder side of the low-side TDM Paddleboard. Order/polarity problems can be handled easily with this type of harness, and recall that we already planned to handle the Global Disable signals with a harness of this style anyway. Since a Rear Paddleboard is not needed on the low side of this chain, the pins emerging here are not a problem. All of the TDM Paddleboards have the same type of connectors, and the bussed signals are terminated at the high side. The radial signals are terminated at the slot where they are used. 2. Per-Bunch Scaler Chain Both the Exposure Group and "Luminosity" Per-Bunch Scaler Chains are similar. They consist only of a bussed component, distributed along chains of Per-Bunch Scaler Paddleboards. These chains are fed from the high side. They differ only in length. These paddleboards have the same problems enumerated above. The solution here is multi-part: 1. The low-side paddleboard must have its offending pins cut off. 2. The high-side paddleboard must use a MALE type, wire-wrap tail connector, with wire-wrap pins similar enough to those on the Panduit connector to allow correct mating to the next-lower Paddleboard. This connector should be a right-angle connector. The bussed signals are terminated on the low side. There are no radial signals to terminate. 3. ST Fired Bus Chain The Specific Trigger Fired Bus Paddleboard Chain is a standard Paddleboard Chain (see item 4 below), with the exception of the terminal 2 cards (which are TRM's). These cards each receive only 64 inputs, so some specialized cabling is required to break 128-bit Specific Trigger Fired Bus up into its 2, 64-bit halves. All of the P2 signals (MSA_In(63:0)) go to the 2 Rear Paddleboards on the high-side TRM: MSA_In(15:0) P2 Paddleboard, J2 connector MSA_In(31:16) P2 Paddleboard, J3 connector MSA_In(47:32) P3 Paddleboard, J2 connector MSA_In(63:48) P3 Paddleboard, J3 connector All of the P3 signals (MSA_In(127:64)) go to the 2 Rear Paddleboards on the low-side TRM: MSA_In(79:64) P2 Paddleboard, J2 connector MSA_In(95:80) P2 Paddleboard, J3 connector MSA_In(111:96) P3 Paddleboard, J2 connector MSA_In(127:112) P3 Paddleboard, J3 connector The TRM Paddleboards are standard Rear Paddleboards, with terminators installed. The Paddleboard behind the FOM++ has 90-degree right-angle wire-wrap tail connectors as in the Per-Bunch Scaler Chain. The other paddleboards are standard "chained" Rear Paddleboards. Standard, 18" section material with two female connectors can be used to connect the TRM's to the rest of the chain. Shorter twist'n'flat, or harnesses made from individual twisted pairs are preferable. Shorter "flat-only" ribbon cable might also be usable. 4. "Typical" Paddleboard Chain In all other known cases, the Paddleboard Chain is made up of "n" identical (typically just standard Rear Paddleboard) cards, with no twist'n'flat connections necessary. Here, the only issue is of space infringement on the low side, so the offending low-side pins are cut off as above. Typically, the feeding card is a Pass Through at the low side, all signals are bussed, and all signals are terminated at the high side.