Standard acquisition modes | General Information |
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Standard acquisition modes
General Information
The standard mode is the easiest and mostly used mode to acquire analog data with a Spectrum A/D board. In standard recording mode the board is working totally independant from the host system (in most cases a standard PC), after the board setup is done. The advantage of the Spectrum boards is that regardless to the system usage the board will sample with equidistant time intervals.
The sampled and converted data is stored in the onboard memory and is held there for being read out after the acquisition. This mode allows sampling at very high conversion rates without the need to transfer the data into the memory of the host system at high speed.
After the recording is done, the data can be read out by the user and is transfered via the PCI bus into PC memory.
This standard recording mode is the most common mode for all an- alog acquisition and oscilloscope boards. The data is written to a programmed amount of the onboard memory (memsize). That part of memory is used as a ringbuffer, and recording is done continu- ously until a triggerevent is detected. After the trigger event, a cer- tain programmable amount of data is recorded (posttrigger) and then the recording finishes. Due to the continuously ringbuffer re- cording, there are also samples prior to the triggerevent in the mem- ory (pretrigger).
When the board is started the pretrigger is filled up with data first. While doing this the board’s trigger de- tection is not armed. If you use a huge pretrigger size and a slow sample rate it can take up some time after starting the board before a trigger event will be detected.
Programming
Memory, Pre- and Posttrigger
At first you have to define, how many samples are to be recorded at all and how many of them should be acquired after the triggerevent has been detected.
Register | Value | Direction | Description |
SPC_MEMSIZE | 10000 | r/w | Sets the memory size in samples per channel. |
SPC_POSTTRIGGER | 10100 | r/w | Sets the number of samples to be recorded after the trigger event has been detected. |
You can access these settings by the registers SPC_MEMSIZE, which sets the total amount of data that is recorded, and the register
SPC_POSTTRIGGER, that defines the number of samples to be recorded after the triggerevent has been detected. The size of the pretrigger results on the simple formula:
pretrigger = memsize - posttrigger
The maximum memsize that can be use for recording is of course limited by the installed amount of memory and by the number of channels to be recorded. The following table gives you an overview on the maximum memsize in relation to the installed memory.
Maximum memsize
ch0 | ch1 | ch2 | ch3 | ch4 | ch5 | ch6 | ch7 | 3110 | 3111 | 3112 | 3120 | 3121 | 3122 | 3130 | 3131 | 3132 | 3140 |
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| 1/1 | 1/1 | 1/1 | 1/1 | 1/1 | 1/1 | 1/1 | 1/1 | 1/1 | 1/1 |
x | x |
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| 1/2 | 1/2 | 1/2 | 1/2 | 1/2 | 1/2 | 1/2 | 1/2 | 1/2 | 1/2 |
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| n.a. | n.a. | 1/2 | n.a. | n.a. | 1/2 | n.a. | n.a. | 1/2 | n.a. |
x | x |
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| n.a. | n.a. | 1/4 | n.a. | n.a. | 1/4 | n.a. | n.a. | 1/4 | n.a. |
x | x | x | x |
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| n.a. | 1/4 | 1/4 | n.a. | 1/4 | 1/4 | n.a. | 1/4 | 1/4 | n.a. |
x | x | x | x | x | x | x | x | n.a. | n.a. | 1/8 | n.a. | n.a. | 1/8 | n.a. | n.a. | 1/8 | n.a. |
How to read this table: If you have installed the standard amount of 8 MSample on your 3132 board and you want to record all eight chan- nels, you have a total maximum memory of 8 MSample * 1/8 = 1 MSample per channel for your data.
The maximum settings for the post counter are limited by the hardware, because the post counter has a limited range for counting. The settings depend on the number of activated channels, as the table below is showing.
(c) Spectrum GmbH | 47 |
