The V126 FEB Control module will be used to generate one of three different FEB event outputs (FebGreen, FebBlue or FebYellow) from the input event Feb Request. FebGreen is the default output and the V126 can be set to output this event indefinitely. FebBlue or FebYellow events will be set to output a finite number of pulses (1-127) with control automatically switching back to FebGreen output when the count cycle is done.

The V126 is designed to reside in a VME chassis, shall occupy one VME board slot (4HP front panel width) and fit into a 6U X 160mm standard Eurocard form factor. The front panel of the V126 will contain connectors for input signals and LED's to indicate output events. The V126 shall require +5V power. The V126 shall communicate with the FEC over the VME back plane. The V126's VME interface shall be a buss slave type and support A16 and D8. The V126 does not support any interrupts. The base address for the V126 will be set using address bits A15 - A7.

There are three inputs to the V126, FebRequest, Permit and a Spare input. All three use Lemo connectors and are optically isolated. Additionally FebRequest input has an LED associated with it.

There are four outputs from the V126, FebGreen, FebBlue, FebYellow and a Spare output. All four use Lemo connectors, are driven with 50-ohm buffers and have LED indicators associated with them.

The following is the memory map for the V126.

The FEB control register, FEB Blue count register and the FEB Yellow count register are all readable/writable from VME.

• The FEB control register (base addr + 0x41) consists of the following bits:

B0 - Sel 0

B1 - Sel 1

B2 - Blue Count Enable

B3 - Yellow Count Enable

B4 - Output Enable Control

B5 - Output Enable

B6 - Permit Enable

B7 - Pulse Control

• Sel 1 (B1) and Sel 0 (B0) select which output pulse is active in the following manner:

• Blue Count Enable (B2) must be set to a value of 1 to enable counting of FEB blue output events when FEB Blue output (sel1-sel0 = 01) is selected. Additionally a count between 1 - 127 inclusive must be entered into the FEB Blue count register (base addr + 0x43).

• Yellow Count Enable (B3) must be set to a value of 1 to enable counting of FEB yellow output events when FEB Yellow output (sel1-sel0 = 10) is selected. Additionally a count between 1 - 127 inclusive must be entered into the FEB Yellow count register (base addr + 0x45).

NOTE: To insure proper circuit function the Blue Count Enable bit (B2) and the Yellow Count Enable bit (B3) are mutually exclusive and both MUST NOT be set to 1 (one) at the same time.

NOTE: When a count cycle (blue or yellow) is complete (the counter decrements from the number entered to zero), the FEB control register bits B3, B2, B1 & B0 will be reset to a value of 0 (zero).

• Output Enable Control bit (B4) selects if the Output Enable bit (B5) is under software control (B4 = 0) or if it will reset when the current blue or yellow count cycle is completed (B4 = 1).

• Output Enable bit (B5) controls if any of the output events (FebGreen, FebBlue or FebYellow) will be generated at the V126's output connectors. This bit must be set to 1 (one) to allow output pulses. Setting this bit to 0 (zero) will disable the output pulses. This bit can operate under software control only by setting bit B4 = zero. However if it is desired to disable all output pulses at the completion of a blue or yellow count cycle then bit B4 must = one and bit B5 will then be automatically reset to zero.

• Permit Enable bit (B6) controls if the Permit input is to be used (B6 = 1) or ignored (B6 = 0). If it is desired to only produce FebGreen output pulses when the Permit link has failed (Permit = 0) then B6 must = 1. Then if the Permit link is valid (Permit = 1), FebGreen output pulses will be inhibited. If it is desired to ignore the Permit input altogether then B6 must = 0. Then all FebGreen output pulses will be produced regardless of the state of the Permit input.

NOTE: The Permit input only affects FebGreen output pulses. FebBlue and FebYellow output pulses are not affected by the Permit input.

• Pulse Control bit (B7) is used to control a spare input/output strictly under software control. This spare I/O is totally independent of the other output pulses. B7 = 1 will enable the spare output. B7 = 0 will disable the spare output.

NOTE: Upon VME power up or VME /SYSRST all bits in the Feb Control register ( base addr + 0x41) will be reset to zero.

• The FEB Blue count register (base addr + 0x43) will be set with the desired number of FEB blue events (1-127) to generate. The count will be set using bits B6 - B0. This register can be read to see what the current count is. Bit B7 will always return as zero.

• The FEB Yellow count register (base addr + 0x45) will be set with the desired number of FEB yellow events (1-127) to generate. The count will be set using bits B6 - B0. This register can be read to see what the current count is. Bit B7 will always return as zero.

NOTE: Upon VME power up or VME /SYSRST both blue and yellow count registers will be reset.