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The Frame Counter Display (1008)
The digits for the frame counter display are sent by means of a four-bit binary coded decimal (BCD) code and eight
strobes, one for each digit. The strobe lines drive non-inverting buffers U9 and U10. U1 through U8 are "smart" seven-
segment displays with internal latches and seven-segment decoders. When strobed, the BCD data on pins 3, 2, 13, and 12
are latched, decoded, and displayed. Refer to the frame counter diagram in Section 8.3.
Framing Board (2276)
The 2276 Framing Board (see also Section 8.12) selects consecutive phototransistors on the pulldown encoder to allow
convenient picture framing by the operator.
System Software
This software theory of operation section offers a deeper appreciation of the basic structure and features of the software.
Some of the functions and features described here may not be pertinent to the current application of the electronic
projector; however, future applications may make use of them. A fuller understanding of the software requires familiarity
with the 6809 assembly language code.
The software that governs the electronic projector system controls the various hardware elements to produce the desired
film motion while handling system communication and fault detection. The interweaving of event-driven and real-time
interrupt routines with background routines for less time-critical functions provides the speed required for projector
operation, along with the robustness of full command functionality. Fail-safe hardware mechanisms back up the software
for those critical functions that protect the film and provide safe operation.
At system start-up, initialization routines set up the hardware and software registers, verify proper system operation, and
begin execution of the basic film motion interrupt routine. A background program, which monitors the system fault status
and the communication ports, is also started. The system is initially in a non-operating state, and must be placed into a
ready condition by specific operator commands. When the projector is in a ready state, it can receive commands either to
affect the movement and projection of film or to change the system state.
The system state is a combination of hardware and software values that are shared among various software subroutines
and store information about previous operations for later use. The selection of an alternate film speed is an example of a
change to the system state. The 35/70 software system can support extensive modifications to projector operation to
enable improvements or implement diverse applications. This flexibility does not compromise system performance.
Software modifications have the additional advantage of eliminating the need for system hardware modifications.
Figure 5.14 provides a high-level flowchart of the system software. Major system variables are listed in Appendix C, the
RAM Assignment Chart.
CHRISTIE INC. - 35/70 Service/PM Manual
CHRISTIE INC. -
July, 1997
5 : T h e o r y o f O p e r a t i o n
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