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6.9.
DISPLAY AND KEYPAD
TECHNICAL DESCRIPTION
The Video keyer U2 is controlled by the KEY signal generated in the LCA.
KEY switches U2 between the program video path and the KEYFILL data.
When the KEY signal is LOW the active video is passed through the keyer.
When the KEY signal is HIGH the KEYFILL data is added to the black level
of the video.
To calibrate the video keyer, connect colour bars from your sync generator
to the Video input loop, of the 4025, and to channel A of your oscilloscope,
and terminate it. Connect the video output to channel B of your scope and
terminate it. Adjust the GAIN trimpot (VR2) so that the output amplitude
matches the input. Adjust the LEVEL trimpot (VR1) so that the inserted
VITC/characters are approximately 550 millivolts above video black level.
6.9.1. LED Displays (7025-31)
A 16 digit alphanumeric display, and a 28 button keypad are contained on
a separate circuit card (7025) which is connected to the 631 VCG module
via a 20 conductor ribbon cable.
The 16 digit display is self scanning and contains its own character display
memory. Data is written to the displays once per frame. Address Latch U1
generates chip enable and address information to the display devices to
allow the MCU to write data to the display and control registers.
The status LED's are controlled by interface drivers U2 and U4. These
drivers are accessed with a serial clock and data stream once per frame.
When all the LED information has been shifted into the drivers, it is latched
there by the LEDSTB signal from the MCU (display header pin 10).
6.9.2. Push buttons (7025-31)
The 28 push buttons are arranged in a 4 x 7 matrix. Data from 7 keys at a
time is latched into U3 by signal SH/LD on U3 pin 1. Address decoder U1
selects which set of 7 switches is latched into U3.
Each time a key is pressed, the MCU firmware generates a key scan code
corresponding to the position of the key in the key matrix.
diagnostics can be invoked by selecting the RAM VIEW from the Toolbox
menu.
The front panel display will show three sets of digit pairs, the
leftmost being the keyboard scan codes. When no keys are depressed,
the key scan code is 00. Pressing a key will show the corresponding key
scan codes, as shown in the table below. To Exit the keyboard test, turn
RAM VIEW off by pressing SHIFT* and then selecting RAM VIEW off from
the Toolbox menu or remove and re-apply power to the unit. See section
5.9 for a complete description of keyboard diagnostics.
Model 4025 Film Footage Encoder Manual
Keyboard
Page 6-25
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