Exposure Control Word
The Exposure Control Word (ECW) defines parameters associated with configuring the instrumentation prior to the exposure. The format of the ECW is shown in table and described in the paragraphs that follow.
| BITS |
| 15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
| DRK |
SPEC |
DEF |
EXEC |
WLI |
|
|
1 |
|
|
|
IND |
|
0 |
|
|
|
AECO |
Dark (DRK)
If DRK is set, the CC takes a dark frame by issuing and timing integrate and readout functions to the
camera interface, i.e., there is no shutter motion. If not set, the CC takes a normal shutter controlled
frame.
Specific (SPEC)
If SPEC is set, the CC uses the index field to get the exposure time from the exposure table. If not set,
the CC gets the exposure time indirectly through the AEC Table for the specific wavelength.
Default (DEF)
If DEF is set, AEC exposures use the default AEC exposure time for the specific wavelength. If not set,
AEC exposures use the most recent AEC exposure time.
Execute (EXEC)
If EXEC is set, the DHC executes the AEC algorithm on image data from this is exposure.
Wavelength Index (WLI)
WLI is a five bit field indicating the wavelength setting for the exposure. The CC uses these bits to access
the Wavelength Table (WLT) to get device configuration information. The uses 5 bits plus the 2 region
definition bits at the current pointing entry in the Pointing Control Table (PCT) to access one of the 128
entries in the Automatic Exposure Table AECT. WLT, PCT, and AECT are described later in this
document.
Index (IND)
IND contains the index to the Exposure Table (ET) for specific exposures, i.e., SPEC is set.
Automatic Exposure Offset (AECO)
AECO contains a number the CC adds to the exposure index prior to getting the exposure time from the
EDT. This number is a seven bit signed number, i.e., bit 6 is the sign bit. This field acts like an
overexpose or underexposure setting on a camera. AECO occupies the same bits as IND. The field is
used as AECO for automatic exposures and as IND for specific exposures.
Last Update: 9/18/97 CC Version 1.26
Name: Michael Levay