WF/PC INSTRUMENT SCIENCE REPORT 90-03:
WFPC and the Take-Data Flag
By Shawn Ewald
September, 1990
Abstract excerpted from the report:
The WFPC microprocessor Application Program AP-17 controls the shutter during long (>3000 seconds) exposures. Usually the program is passive, but when the spacecraft take-data flag falls, AP-17 will close the shutter. This report examines the telemetry data associated with an exposure which was while the take-data flag changed state. AP-17 affects total exposure time and shutter blade parity. The latter effect is important for preflash calibration.
The complete report (PDF 0.14 MB) is available.