IV. RESULTADOS Y DISCUSIÓN
4.3. CALIDAD DE LA PIEL DE CUY ( Cavia porcellus ) CURTIDA CON
In order to cope with the fast data rate, a 486 DX PC (33 MHz, the fastest available at that time) with a fast graphics capability and High-Speed CMOS (HC) series ICs were required. The strobe, clock and data signals form a synchronous interface, and make the task of recreating a parallel stream easy, for interfacing to the parallel interface of a PC.
Chapter 3. Science Data Display Adapter 46 Strobe o Clock 0 Data 0 80 0 ns (1.25 M H z) 1 1 1 D etector ID U ndefined data — . ! 1 DO D 12 1 D l l 1 D IO 1 D9 1 D8 D7 1 D6 1 D5 1 D 4 1 D3 I D 2 I D1 1 DO D 12 1 1 ^ --- M SB L S B | ---►! 11.2 ps
(a) M axim um R ate (8.9 x 10“* events / second)
Strobe o Clock 80 0 ns (1.25 M H z)
: ruxrLrurun_
Data 0 I D5 I D4 I D 3 I D 2 I D1 I DO I . . . [ . . . ] LSB D etector ID U ndefined data D 12 I D l l I D IO I D 9 I D8 ■ 4 .8 p s (b) M edium Rate I Strobe o Clock 0 8 0 0 ns (1.25 M Hz) I U ndefined data Data 0 I D3 I D 2 I D1 I DO I j I j LSB 1 D etector ID D 12 D l l D IO M SB > 8 p s (c) Slow RateFigure 3.8 Timing diagrams of the interface signals at various event rates. All three signals from the GIS are differential to minimize noise, but the signals shown are the single ones at the outputs of the differential amplifiers (refer to the block diagram in Figure 3.9). There is also one redundant line for each of the signals, which are not shown. The clock runs at 1,25 M Hz which determines the maximum event rate. Note the difference in lengths of the strobes remaining HIGH depending on various event rates. ‘Shadow ed’ data area represent ‘undefined’ data.
Chapter 3. Science Data Display Adapter 47
The essential SDDA display requirements were as follows:
• To display spectral lines on a PC screen for one detector at a time, with sufficient resolution to display the full 2048 possible line elements (the vertical scale representing the count rates). As a typical PC screen is only 640 pixels wide, the display needs to be wrapped down the screen to make it fit. The 2048 horizontal resolution represents the positions of the dispersed incoming photons along the detectors (i.e. wavelengths of the photons).
• Reduce the resolution of the display to show the spectrum of photons from all four detectors on one screen, ensuring that all lines present are actually displayed. After viewing the whole spectra at the same time, an operator can select one specific detector for the full resolution; the displays can be switched back and forth.
• The vertical scale of the display needs to be switched between logarithmic and linear scales, which range from 0 to 9 x 10"^ events per second. The logarithmic scale provides a better view of the spectrum when the difference in the count rates on different positions along the detector is large, whereas the linear scale is normally used for a precise comparison among different wavelengths or positions along the detectors. • The maximum on the scale should be operator adjustable to cope with very high or low
count rates. The length of the lines (count rates) can be scaled up or down for low or high count rates, respectively, to fit the spectrum within the PC screen window.
• There should be a cursor that, when positioned on a line, displays the line number and the count rate of the line. This feature allows an operator to find out the exact count rates of photons on specific wavelengths.
• The display needs to be printed out. This makes documentation of the results easier. The display can be printed out on HP LaserJet printers.
• The display needs to be saved and loaded in and from a file. The display options (scaling factor, etc.) and the data can be saved in a file for later uses of displaying, printing and so on. A saved file can be loaded to be displayed again on a screen. The
Chapter 3. Science Data Display Adapter 48
exact display with the same options, that are previously saved, is restored, and an operator can apply new options to the display including printing out the display.
• There should be an accumulation mode. In a normal mode, the display is refreshed every half a second (0.52428 seconds, refer to Section 3.4.4.4). In case of low rate data, it is hard to see the spectrum lines even when the lines are scaled up. By accumulating the data without refreshing the screen, low rate data can also be viewed clearly.
• There should be a reference line next to the display. The reference line is set at 3000 counts per second. By comparing the length of the reference hne with the data spectrum lines displayed, it is possible to get a rough idea of the count rates on various positions (1 to 2048) along the detectors without actually halting the process to find out the count rates by placing a cursor on various positions.
• The dead time needs to be calculated and displayed. It is not possible to collect any data from the GIS while the PC is displaying collected data on a screen. The dead time
(%) is given by
Dead Time ( % ) = X 100 % n n
ttotal
where ttotai is the total time taken to collect and process the data and display on a screen and tdispiay is the time taken to process and to display the data. As the data are always collected for 0.52428 seconds (see Sections 3.4 and 3.5 for detail), tdispiay is ttotai - 0.52428 seconds. Therefore, the faster the PC can display data, the shorter the dead time.