Front-end Links Specification Sheet


(1) Overview

The ROD-ROB link, also called Read-out Link, is the link that connects the Read-out Drivers to the Read-out Buffers. Both the ROD and the ROB will be outside the cavern, which means that there are no strict radiation or power requirements. Around 1500 serial links are required, each one running at 100 MByte/sec over a distance of up to 200 m. The links use flow control, which means that fibres are needed in both directions. The S-LINK project has made a start of defining a read-out link and has built several links, interfaces and test tools. Those links are actively being used and feedback is being collected from testbeams. All results from the S-LINK project will be invaluable for the final specification and design of the Read-out Links.

(2) Notes and Terminology

See Template Front-end Links Specification Sheet.

(3) ROD-ROB Link Specification Sheet

Physical characteristics
Number of links 1500 1500
Length of links 200 m
Grouping of links 1 1
Connections along a link 0
Fibre type conserved  Yes
Redundant links No
Data characteristics
Data format (width) 32 + 1 bit 1 bit (flow control)
Speed 100 MByte/s (1998)
160 MBytes/s (2000)
Clock  40 MHz
Redundancy No
Test mode Yes Yes
Link down indication Yes Yes
Max detectable BER 10-12
Error correction No (Error detection: yes)
Tolerable MTBF
Acceptable no. dead after 10 yrs 40
Eye safety issues Yes
Access considerations  No
EMC considerations Yes
Timescales 2003: production
Milestones 2002: pre-production link 
2000: final URD
Work needed to complete solution Reduce size and cost 
Decide on technology 
Collect feedback of users 
of S-LINK as input to URD
Receiver connector 5 cm2 * 10 mm
Transmitter connector 5 cm2 * 10 mm
Cabling 150 cm2 for all 1500 links
Receiving device -
Transmitting device -
Receiver electronics 50 cm2 * 5 mm
Transmitter electronics 50 cm2 * 5 mm
Whole receiver  3 Watt
Whole transmitter 3 Watt
Receiving device No
Transmitting device No
Receiver electronics No
Transmitter electronics No
Receiver connector No
Transmitter connector No
Cabling No
Receiving device CHF 50 CHF 50
Transmitting device CHF 50 CHF 50
Receiver electronics CHF 75 CHF 75
Transmitter electronics CHF 75 CHF 75
Receiver connector (in receiving device) (in receiving  device)
Transmitter connector (in transmitting device) (in transmitting device)
Cabling CHF 100 CHF 100

(4) Proposed Solutions

22 April 1998

Currently (April-1998) the S-LINK specification is being used in several ATLAS ROD/ROB link prototypes  (e.g. MDT, TRT, TileCal). The feedback from those prototypes and from other users outside ATLAS (e.g. NA48, COMPASS) is being collected. Until now no major comments are received, which means that the S-LINK specification can be used as a solid basis for the final ROD-ROB link specification.

The components (not including the PCB) of S-LINK link cards using fibre optic drivers cost CHF 635 in low quantitites. The optical transceiver is taking more than half of this cost. In the S-LINK project we have several means of reducing the cost to the required CHF 250 per side. We will start using Gigabit Ethernet components (electrical transceivers and optical transceivers) which are likely to become much cheaper than the Fibre Channel components used now. Also we will be able to integrate more components as fast enough programmable chips are becoming available. A reduction in cost may be obtained if instead of seperate optical devices for each ROD-ROB link, we will combine the electrical links of twelve RODs and use a single 12-channel electrical to optical transceiver such as the Siemens PAROLI to drive a ribbon fibre with MT connectors. All those possibilities of reducing costs will be used in the ongoing S-LINK project and will have been tested before being used in the final ROD-ROB link.

Update 13 March 2000

The components (not including the PCB) of ODIN link cards using fibre optic drivers cost CHF 411 in low quantitites. This link can send data at 128 MB/s, while a more expensive version can send data at a speed near to 160 MB/s. The new Technical Proposal requires now a link speed of 160 MB/sec, which was before specified as 100 MB/s only. As this means new generation fibre-optic components are needed (2.5 Gbps instead of 1.25 Gbps), this will impact the costs of the links which is not reflected in the the table above. However, as we believe that not all links need to be running at 160 MB/s, we will keep having versions of the S-LINK that run at speeds over 100 MB/s, using cheaper components.

Update 27 October 2000

During the 2nd ATLAS ROD workshop the ODIN link was presented (1MB pdf). It was proposed to make the ODIN/S-LINK protocol logic available as a core function. This core can then be integrated with other logic on the ROD or ROB, which has the following advantages: The cost of the read-out link will be reduced to the price of the transmitter and receiver chips and the fibre-optic transceiver. This is CHF 306 in single quantity for the 128 MB/sec version (CHF 521 for the 160 MB/sec). Most ROD and ROB designers have shown interest for integrating the link logic on their boards.

Erik van der Bij - CERN/EP - 27 October 2000