Character Generator Logic (5200-35) - evertz 5010 SIE Instruction Manual

Model 5010-SIE Source ID Encoder Manual
To calibrate the video keyer, connect colour bars from your sync generator
to the Reader Video input loop of the model 5010 and to channel A of your
oscilloscope and terminate it. Connect one of the video outputs of the
model 5010 to channel B of your scope and terminate it. Adjust the GAIN
trimpot (VR3) so that the output amplitude matches the input. Adjust the
CHAR LEVEL trimpot (VR2) so that the inserted characters are
approximately at the peak white video level.

4.3.5. Character Generator Logic (5200-35)

The majority of the logic for the character generator functions is contained
in a programmable logic device (LCA) U36. Its program is loaded from
EPROM U35 on power up. The character display is formatted to display 28
(32 for PAL) rows of 32 characters each in the tiny size, 14 (16 for PAL)
rows the small size, and 7 (8 for PAL) rows in the large size. Each of the
character positions corresponds to one location in static RAM 37. The
MCU writes characters into specified locations in the RAM corresponding
to the position of the characters on the screen. RAM locations are scanned
during each television field. Valid characters address corresponding
sections of the character EPROM U35 and are loaded into the LCA one
byte (8 bits) at a time. Each byte corresponds to either the left or right half
of a character pixel line. The internal logic in the LCA controls how many
lines per character and how many character lines there are on the raster
according to registers set by the firmware.
The character data is clocked out of the LCA on the VCGWHITE output
(U36 pin 73). A special character with all bits set to 1 is written into all
positions of the RAM where no characters are to be displayed. These
characters disable the keyer by the VCGKEY signal generated in the LCA
(U36 pin 79). When other characters are present the VCGKEY signal
becomes active, allowing the characters to be keyed into the video signal.
The character data is clocked out of the LCA with the dot clock, so that the
pixel width is not dependent on propagation delays in the LCA. The pixels
are presented to the video keyer U40 through CHAR LEVEL trimpot VR2.
A control register in the LCA selects whether the characters will be white or
black and whether they will be keyed into a contrasting background.
Character style selection is accomplished by the on screen programming
menu.
The pixel oscillator consists of monostable U32b and associated
components. The oscillator frequency which determines horizontal size of
the characters is adjusted by the digital trimpot (NOVPOT) U34 and
associated components. The MCU writes different values to the NOVPOT
which control the adjustment input to voltage regulator U33, which in turn
sets the voltage present for the RC timing network of the monostable. The
starting position of the characters at the left of the screen is determined by
monostable U32a. The left position of the characters is adjusted by trimpot
VR1.
TECHNICAL DESCRIPTION Page 4-9