Raytheon DIDS-400 Series Technical Manual page 196

DIDS-402-2AMI3
4-26 MONOSCOPE DEFLECTION AMPLIFIER A3
The purpose of the m.onoscope deflection am.plifie r is to convert digital
character codes arriving from. Display Logic Board Al3 to analog deflection
voltages. These analog voltages are then used to position the m.onoscope scan
to a corresponding character sym.bol on the m.onoscope target. In addition to
positioning the scan, other signals developed on A3 cause the scan to sim.ul-
taneously sweep up and down and across the character symbol.
The m.onoscope deflection am.plifier is com.posed of the following circuits:
X and Y digital-to-analog (D/ A) converters
X- and Y -deflection amplifiers
X- and Y - skew correction
Ramp and rn.inor vertical sweep generation
Unblanking pulse generation
4-26. 1 X and Y Digital-to-Analog Converters
As previously stated, the monos cope target is com.posed of 96 separate
character symbols arranged in an 8-row, 12-column coordinate system. The
monoscope scan is directed to a particular row on the target by a Y-axis deflec-
tion voltage. This voltage is developed by sumrn.ing the binary values of the three
LSB's of a character code held in the CR register. Conversely, the monoscope
scan is directed to a particular column on the target by an X-axis deflection
voltage. This voltage is developed by summing the four MSB's of a character
code held in the CR register. The particular character being scanned at any
given moment is determined by the intersection of the X- and Y-axis analog
voltages. The m.anner in which these analog voltages are developed is described
below (see Raytheon Drawing 425100).
The four MSB's of the character held in the CR register are coupled to the
monoscope deflection amplifier over input lines DAX8, DAX4, DAX2, and DAXl.
These bits are applied to a weighted summing network formed by diodes CR2
through CR5, four similar diodes in I-C AI, and resistors R51, R71, R72, and
R 73. The binary value of the four MSB' s connects a specific re sistive network
between a reference regulator, AS, and the input to X-axis deflection amplifier A2.
Depending upon the characte r code held in the CR register, current flows
from the reference regulator through one, two, three, or all four of the weighting
resistor s. The analog voltage applied to the input of A2 is therefore proportionate
to the binary value of the characte r code s for the MSB' s. The analog voltage
developed in this manner is applied to A2 in coincidence with the ramp signal.
The three LSB's of the character held in the CR register are converted
in a similar manner. These bits are applied to the monoscope deflection
amplifier over input lines DAY4, DAY2, and DAYl. The Y-axis sum.ming
network is formed by diodes CR6 through CR8, three sim.ilar diodes in I-C AI,
4-154