Yes this is correct. Anyhow, even if it would be working, you would not be happy with it. After having designed ~10 boards with the DRS4 chip, I learned the hard way that any digital activity on the board during the sampling phase is strictly forbidden. You see crosstalk up to 100's of mV in some cases (with a preamplifier on the board, 10-20mV without preamp). So rule #1 is to keep the board as "quite" as possible when sampling the input. If you would readout the odd channels of the DRS4 during sampling of the even channels, you would probably get so much crosstalk that the samples are almost unusable. Even if you would do this with two DRS4 chips next to each other, you have to make sure to put proper grounding between the two chips, and operate them completely independent (like each one has it's onw contol lines going to the FPGA). Designing such boards is not so easy and takes lots of experience from the layouter.
Stefan
| Jonathan Bradshaw wrote: |
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Hi Stefan
Just so I'm 100% clear; is there no reliable way to perform 2 segmented captures with a single DRS4 IC?
While not a showstopper, this is a bit disappointing.
| Stefan Ritt wrote: |
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This is correct. Setting A0-A3 to 0b1101 multiplexes the Shift Write Register to SROUT, so you will either a "0" or a "1" depending on which of the two channels was written last.
Your segmented capture does unfortunately not work. Due to a bug in the silicon, the first (e.g. even) written channel gets half overwritten when you start sampling the second (odd) channel. I should remove that from the documentation.
Furthermore, reading the chip while writing on the "other side" introduces quite some additional noise. The recommended way to do simultaneous reading and writing is therefore to use two separate DRS4 chips and split the input signals to both chips, then read from one chip while writing to the other chip. This keeps the crosstalk at a minimum and both chips run at full performance.
Stefan
| Jonathan Bradshaw wrote: |
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Hi all
We're building a product which will use two different operating modes; firstly a long capcture using channel daisy chaining (2048 samples) and secondly a segmented capture (2 separate captures of 1024 samples each).
For the long capture, I'm looking to capture 2048 samples for 4 channels. Therefore I configure the Write Shift Register to 0b01010101 and the Write Config Register to 0b11111111. During capture with DWRITE=1 the Write Shift Register will update. Am I correct that once the capture is done and DWRITE=0, I can set A3..0 to 0b1101 and simply read the value of WSROUT to tell the difference?
For the segmented capture, I'm looking to capture 1024 samples for 4 channels on a first tirgger pulse, followed by 1024 samples for 4 channels on a second pulse. Therefore I configure the Write Shift Register to 0b11111111 and the Write Config Register to 0b01010101 and set DWRITE=0 to capture. After the first trigger I set DWRITE=0 and need to update the Write Config Register. Do I need to write in a whole 8 bits to the Write Config Register (i.e. 0b10101010), or can I just shift in a single new bit (value 0b0)?
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