
manipulation in the field-of-view etc. and then revert to a full-resolution 12f/s color image after
determining an image of interest.
7.7 SLOW
SCAN
Slow scan: The read noise of a CCD is significantly affected by the scanning rate. Some users
wish to improve the read noise by slow-scanning the CCD. This is provided in the camera by
means of a clock multiplexer scheme; the user selects which one of the four (4) clocks is to be used
as the pixel clock.
Note: This selection affects all the internal clocks, since the entire timing logic runs on the selected
clock. Therefore, all exposure values etc. will be scaled accordingly.
The slow-scan mode of the camera is set via the SLW command. There are four valid arguments to
this command {01, 02, 04, 08}. When one of these commands is issued by the host-side software,
the mode control bits are set as shown in the table for 2
µ
sec. The mode control bits then revert to
the setting (1 x x x) just prior to the slow-scan command.
Command Code
Description
Frame Rate
(LVDS)
Clock (LVDS)
SLW 01
Fast pixel clock divided by 1
12f/sec
20 MHz
SLW 02
Fast pixel clock divided by 2
6f/sec
10 MHz
SLW 04
Fast pixel clock divided by 4
3f/sec
5 MHz
SLW 08
Fast pixel clock divided by 8
1.5f/sec
2.5 MHz
Table 7.7-1: Slow-scan mode commands
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