Siemens MAMMOMAT NovationDR, Installation Instructions Manual, Page: 20 / 95

Theory of Operation
February 5, 2004
2-3
Communication Between the PXCM and the Generator
During an Exposure
The interface between the DirectRay Power and X-ray Control Module (PXCM) and
the Generator consists of seven hardware signals and regular exchange of
messages over an RS232 serial communication link.
There are two exposure operating modes: Manual and Automatic Exposure Control
(AEC). The exposure sequence is slightly different between the two modes. The
main difference is that the AEC exposure actually consists of two exposures: a
short pre-exposure; followed by the measurement, calculation, and transfer of the
required mAs value from the PXCM to the Generator; followed by the main
exposure.
Figure 2-2 on page 2-4 and Figure 2-3 on page 2-5 show the signals and their
relative occurrence in time.
NOTE: The PXCM is also referred to as the “brick.” Therefore, you will see the terms “PXCM” and
“brick” used interchangeable throughout this topic.
Additional Information About AEC Mode
During AEC mode:
1. A 5-mAs pre-exposure is made.
2. The actual mAs of the pre-exposure is sent from the Generator to the PXCM in
a code-S message.
3. The PXCM collects the resulting pixel values, binned together in super pixels
(128 x 128 pixels), from the Detector.
4. Using these super pixel values and the exposure parameters (for example, kV
and speed, supplied in the code-X message) of the exposure, the PXCM
calculates the required mAs value (which depends on the desired pixel value)
to be used for the main exposure.
5. The calculated mAs value is made available to the Generator by a code-B
message from the PXCM.
6. Once the calculated mAs value has been set up in the Generator, the Generator
sends a code-Y message to the PXCM.
7. The PXCM again activates its DR_DET_RDY_FOR_EXP_ signal; the
Generator starts the grid and, when in position, starts the actual exposure.