New Trigger Bus Media

General IO interface

To make the DaqNetwork independent from any media, a standard IO interface is proposed. The interface follows the principle, that data words are never pushed into the next stage, but always offered and read be the next stage. In detail, the interface should look like:

Line Decription
INT_DATAREADY_OUT Data word is reconstructed and ready to be read out by the internal logic
INT_DATA_OUT[0...55] Data word
INT_READ_IN Internal logic is reading from the FIFO
INT_ERROR_OUT[0..2] Status bits
INT_DATAREADY_IN Data word is offered by the internal logic or FIFO
INT_DATA_IN[0...55] Data word
INT_READ_OUT Media interface reads a word

(the INT_ERROR_OUT will be used only for the 1st output)

As one can see, there are 2 symmetric directions: One for the direction to the internal logic, one for the data direction to the media. All entities of the DaqNetwork should follow this principle (sometimes however one one-directional, and the width "DATA_WIDTH" might change)

The 8 missing spare bits to complete 64Bit might use for additional error detection/correction if needed.

Meaning of the error bits:

Bits Description
000 Data word OK
001 Transmission error from the 8B/10B encoding
010 Transmission error, reconstructed by additional bit
011 Fatal error, not recoverable
100 Media not connected


To avoid the big register logic of all entities which are using really big buses, the generic "SLICES" should be used.
  • SLICES=0: Do not use slices, only the big bus
  • SLICES>0: Scramble the bus into several slices

In addition, the generic "BUS_WIDTH" has to be used. It is very clear, that for the SLICES=0 the BUS_WIDTH have to match the DATA_WIDTH. Otherwise, the bus bits have a different meaning: The first bits are the slice number, so if SLICES=4 (matching to 100MHz with the optical link), 2 bits are needed. In addition, for 56 data bits, 14 bus bits are needed in addition. This makes 16 bits!

The use of an optical links has many advantages:

  • No charge flow
  • Long cable connections (1km!)
  • Fast
  • Standard technologie (SFP), many vendors

We will use the TLK2501/TLK1501 as a Serdes chip: 16 Bit data bus, error and link detection makes debugging much easier. In addition, the 8B/10B encoding allows to send special symbols, like commas, carier extend, errors. This allows to separate the frames and synchronize state machines of the transmitter and receiver.

The frame content of the NewTriggerBusNetwork is always fixed on 64Bit (with 56Bit needed data bits for the protocol), thus it makes the decoding very easy. In addition the 8 remaining bits could used the protect the most important 2*4 Bits (transported in 4 TLK frames) using the 4-7 Hamming code. These bits can even be reconstructed if a word is completely corrupted, the data content is then lost, but who cares...

SCSI cable and trb add-on lvds links.

A standard SCSI cable is used for the connection of the AcromagModule. From the 32 IO lines, 16 lines are used for each direction.
Line(s) Signal
1-13 Data0-12
14 CLK
15 carrier
16 Parity
As it can be seen, with 13 data bits, 65 data bits can be transferred in 5 frames (9 bits can be used for error checking and correction). "carrier" is 1 for data words, and 0 for control words (like idle), needed for frame synchronization. Parity can be used for additional error detection. The order of the signal on the cable or the addon connector depend on the clk input pins and might differ for the 2 cases.

Additional Media?

* RJ45:

Advantage: 4 twisted pair lines, off-the-shelf cables

Two pairs can be used for downstream (to the endpoints), and 2 for upstream (to the master). This allows to use always one line for clock (if needed) and one for data. LVDS signals should be used, the clock frequency should be choosen that 100m cables could be used.

Signal Pin Color of Line
UpCLK+ 1 white to green
UpCLK- 2 green
UpDATA+ 3 white to orange
DownCLK+ 4 blue
DownCLK- 5 white to blue
UpDATA- 6 orange
DownDATA+ 7 white to brown
DownDATA- 8 brown

The use of the signals in this way makes sure that even if by accident a crosover cable is used, only CLK and DATA of one direction is mixed.

-- TiagoPerez - 20 Nov 2006
Topic revision: r11 - 2009-12-31, JanMichel
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