The LeCroy VME Model 1176/EXP2 Hit Expander is a companion module to the VME Model 1176 and the CAMAC Models 2277 and 3377, as well as the FASTBUS Models 1876, 1877 and 1877S Time Digitizers. These new TDCs have 1 nsec or better resolution, double hit resolutions better than 20 nsec, a full scale of at least 32.7 µsec and have a 16 hit deep pipeline for each channel. When used with any of these expanders, these TDCs experi ence an improved double pulse resolution (to 2 nsec) and the pipelined hit depth is increased to at least 64 hits per input. This is accomplished by routing one input signal to several TDC channels, creating a composite TDC channel with improved performance. The expander can also be used in a stand-alone mode as a prescaler or a rate reducer with a divide by 8.
When used with the 1176, 1876, 1877, 1877S, 2277 or 3377 TDCs, the 1176/EXP2 has two operating modes controlled by a front panel switch.
With the switch in the L.E. ONLY (leading/rising edge only) position, the combined modules (Expander and TDC) form a two input, rising edge only, composite TDC having the same resolution as the TDC module. A set of 7 flip -flops for each channel divide the incoming pulse stream by 8, and drive 8 inputs of the TDC module. The TDC module must be set to record rising edges only. This gives each input a depth of 128 pulses (hits). The double hit resolution is 2 nsec.
With the switch in the L.E.-T.E. (leading/rising-trailing/falling edge) position, the combined modules have only a single input, with both rising and falling edge detection. The TDC module must be set for rising edge recording only. This gives an input with a depth of 128 pulses (256 hits). The double hit resolution is 2 nsec.
The 1176/EXP2 maximum input pulse rate is greater than 450 MHz, typically 500 MHz. The
same-edge double hit resolution is 2 nsec, and the minimum width is 1 nsec. The EXP2 uses
another layer of flip-flops and a faster logic family to achieve the higher speed.
The 1877, 1877S and 3377 will correctly record a long pulse train at the maximum rate. The 2277, 1176 and 1876 will record a short burst at the maximum rate, but the long term average rate must be less than 1/2 of the maximum rate.
When the data are read from any of the TDC modules, there are 96, 32 or 16 channel numbers, not 8, 4, 2 or 1. The simplest way to deal with this is to mask the 3 least significant bits of the channel number, treating channels 0 through 8 as channel 0 for example. Then sort all of the data for this new composite channel 0 into time order. For the EXP2, the TDC module channels 0-7 are the leading edge, channels 8-15 are the trailing edge.
This module uses the respective crates for power and mechanical support only. There are no VME commands required for operation. There is no clear; the modules are free running.
Some input and output examples for the expander modules.
Copyright© March 1997. LeCroy is a registered trademark of LeCroy Corporation. All rights reserved. Information in this publicaction supersedes all earlier versions.