PPA55xx Quick User Guide
Page 79
PPA CAPTURE MODE
To perform capture mode tests it is necessary to use a PPA5510 or a PPA5530 and upgrade the
Firmware within the instrument to either PPA5512 (Single Phase) or PPA5532 (Three Phase)
Capture mode operates as a sub function of the normal oscilloscope mode – enable “capture mode” in
the application menu. Data is then stored in a 50000 byte circular buffer per channel. Set the trigger
mode to single shot and trigger as normal. Extracting the sample data is performed using the
CAPTUR? command. Data is returned in 200 lines per channel of 250 values.
The sample capture data reply is consistent with multiple lines of IEEE488.2 “definite length arbitrary
block response data”. So each line of data should return as follows:
[#3503] [h1][h2] [d1.1][d1.2][d2.1][2.2]……[d250.1][d250.2] [error] [CR] [LF]
Each line consists of:
5 bytes that represent #3503 (ASCII)
2 bytes that represent the Header bits including channel number [h1][h2]
500 bytes that represent the actual data. 250 pieces of data each made up of 2 bytes. d1.1 is data 1
bit 1, d1.2 is data 1 bit 2, d2.1 is data 2 bit 1, d2.2 is data 2 bit 2 etc
1 byte that represents the error checking bit [error]
1 byte that represents Carriage return [CR]
1 byte that represents Line Feed [LF]
Each 8 bit byte has the msb set in order to prevent any misinterpretation of data within drivers and
software which otherwise could mistake data for carriage return etc. so 14 bit data values are
returned.
The meaning of the 2 header bytes is as follows:
(header h1) (header h2)
[1][c2][c1][c0][0][0][0][a7] [1][a6][a5][a4][a3][a2][a1[a0]
^ first bit ^ first bit
And as for the meaning of each of the bits:
[0][0][0] these 3 bits are not used and can be ignored.
[c2][c1][c0] are the channel number
4 2 1 so the channel number can be a number between 0 and 7
[a7][a6][a5][a4][a3][a2][a1][a0] are the line number.
128 64 32 16 8 4 2 1 so the line number can be a number between 0 and 255.
The meaning of each pair of data bytes is as follows:
(data d1.1) (data 1.2)
[1][d13][d12][d11][d10][d9][d8][d7] [1][d6][d5][d4][d3][d2][d1][d0]
^ first bit ^ first bit
[d13] [d12] [d11] [d10] [d9] [d8] [d7] [d6] [d5] [d4] [d3] [d2] [d1] [d0] contain the data [a number]
8192 4096 2048 1024 512 256 128 64 32 16 8 4 2 1
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