Service manual

LUMISCAN ACR-2000 SERVICE MANUAL - SECTION 4.0 THEORY OF OPERATION
4-8
Control During Scanning
During the scanning process the DCB generates the timing and synchronization signals and transfers the
image data into image memory as it becomes available. There are three clock generators and three
counters: Scan Clock, Film Clock, Pixel Clock, Delay to 1st Pixel count, Pixels per Line count, and Lines
per Image count. These are each described briefly below.
The Scan Clock is a continuous clock signal derived by dividing 10Mhz. It is used to control the line scan
repetition rate and to synchronize the beginning of each scan sweep (Start of scan, or SOS). The actual
linear rate during each sweep is controlled by the Data Acquisition board. For the 135 the Scan clock is set
for a 50 Hz scan rate and should never be changed.
The Film clock is a continuous clock signal derived by dividing 10Mhz. It is used as the reference for a
frequency-controlled servo motor driver which controls the film transport motor. The plate speed is directly
proportional to this frequency.
The Pixel Clock is a gated trigger signal derived from 40Mhz. The trigger signal is sent to the DACQ
during each scan line after the completion of the Delay to 1st Pixel count and until the completion of the
Pixels per Line count.
The Delay to 1st Pixel counter counts the Pixel clocks, beginning at SOS (Start of Scan) and terminating
when its preset count is reached.
The Pixels per Line counter is enabled at the termination of the Delay to 1st pixel count and counts Pixel
clocks, terminating when its preset count is reached. If enabled an interrupt request will be generated at
count termination.
The Lines per Image counter is enabled at the beginning of a scan and is incremented at the end of each
scan line, terminating when its preset count is reached. If enabled an interrupt request will be generated at
count termination. The usual value for this counter is 65,535 (maximum), which effectively disables this
control and permits the Isfilm (plate present status) signal to be used to control acquisition.
Interrupt Requests
There are four possible sources for interrupt requests by the DCB: Last pixel in line, Last line in image,
Change in Isfilm (film entering or leaving optical path), and Event 0, which is used for the Abort switch.
Each can be independently enabled and cleared.