This text is stolen from Michael Bhmer:

http://www-hades.gsi.de/daq/rc99/richel_page.html

A summary of the HADES trigger codes

On this page you can find a summary of all information which is related to the new trigger codes which were introduced into the HADES DAQ system with the new CTU design.

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Trigger codes and types The new CTU support a different set of trigger codes on each LVL1 and LVL2 bus. In general, there are trigger codes which can be generated by hardware lemo connectors and others which can only be generated by software.

Trigger codes and where you can generate them

Some words before reading the table:

• Source tells you where to generate the trigger: Software means by writing some stuff into the CTU, Lemo (X) by applying a pulse on the lemo number X at the CTU. Lemo connectors are numbered 1 to 12, starting with 1 on the uppermost connector and stopping with 12 on the lowermost connector on the famous CTU trigger module.
• LVL2 (+) is the trigger code which is automatically generated by the CTU in a standalone system or the Matching Unit (MU) in a common system. This code carries a positive decision.
• LVL2 (-) is the trigger code which is automatically generated by the CTU in a standalone system or the MU in a common system. This code carries a negative decision.

LVL1 bus					LVL2 bus
Code	Name	Usage	Source	Reaction	(+)	(-)	Name	Reaction
0x0	ILLEGAL	---	---	error	---	---	---	---
0x1	NORM1	generate data	Lemo (1)	data	0x1	0x9	NORM	follow decision
0x2	NORM2	generate data	Lemo (5)	data	0x1	0x9	NORM	follow decision
0x3	NORM3	generate data	Lemo (6)	data	0x1	0x9	NORM	follow decision
0x4	NORM4	generate data	Lemo (7)	data	0x1	0x9	NORM	follow decision
0x5	NORM5	generate data	Lemo (8)	data	0x1	0x9	NORM	follow decision
0x6	SPEC1	---	Lemo (9)	cal.	0x2	0xa	SPEC1	decide yourself
0x7	SPEC2	0.1Hz offspill	Lemo (10)	cal.	0x3	0xb	SPEC2	decide yourself
0x8	SPEC3	---	Lemo (11)	cal.	0x4	0xc	SPEC3	decide yourself
0x9	SPEC4	10Hz	Lemo (12)	cal.	0x5	0xd	SPEC4	decide yourself
0xa	SPEC5	---	Lemo (2)	cal.	0x6	0xe	SPEC5	decide yourself
0xb	ILLEGAL	---	---	error	---	---	---	---
0xc	ILLEGAL	---	---	error	---	---	---	---
0xd	BEGRUN	distribute first tag	software	store tag	---	---	---	---
0xe	ENDRUN	---	software	empty pipes	---	---	---	---
0xf	ILLEGAL	---	---	error	---	---	---	---
---	---	---	---	---	0x0	0x8	ILLEGAL	error
---	---	---	---	---	0x7	0xf	ILLEGAL	error

Rules of engagement part I (or: EtraxEPICSHowTo LVL1 bus)

For the LVL1 bus, there are some rules on how to react on triggers coming into the DTU:

1. Set your own busy as soon as a trigger on the LVL1 bus is entering your DTU.
2. Decide what to do by looking at the whole trigger code.

It is not right that on all trigger codes data is produced in the readout electronics. The reaction on trigger codes on the LVL1 bus is as follows:

• NORMALx triggers: generate data in your electronics
• SPECx triggers: generate EITHER real data OR calibration data OR fake data, depending on your system's abilities and needs.
• ILLEGAL triggers: generate a LVL1ERROR and stop all further activities.
• BEGRUN trigger: store trigger tag for distribution with the next trigger, do no further action.
• ENDRUN trigger: (optionally) try to get all data from the pipes on your frontends to the IPUs

Rules of engagement part II (or: EtraxEPICSHowTo LVL2 bus)

In earlier revisions of the HADES trigger system all LVL1 trigger were reproduced 1:1 on the LVL2 bus, except that the decision bit was set according to the MU's decision. This is not longer the case. The LVL2 bus has been simplified and now only transports the readout triggers together with the decision. To take into account that some detector systems use the new SPECx triggers for calibrating, while others don't, the reaction on the readout triggers on the LVL2 bus is to be specified:

• NORM: every DTU has to follow the MU's decision.
• SPECx: decide yourself what to do. The MU will probably generate only positive decisions, as calibration triggers which are killed without being readout are nonsense, so detector systems which do not use online calibration can (and are officially allowed to) generate their own decision. The event builder will take care of the "missing" subevents.
• ILLEGAL: generate a LVL2ERROR and stop all further activities.

-- MichaelTraxler - 15 Apr 2005