Line Control Card (Location C2); Base Logic Card (Location 02) - IBM 3279 2A Maintenance Information

3.7 Line Control Card (Location Cl)
The line control card (see lower part of Figure 3-6)
contains:
• Circuits to handle transmission and reception of
data down the coaxial Une to the control unit.
• Main oscillator (14 MHz), dot counter and
feature clock.
• A serializer that converts the ROS outputs from
the base logic card to drive the three video
outputs.
• Test circuits that force colored bar patterns on
the screen adjustments.
(Video Output Facility only) Circuits that
produce red, blue, green, and sync signals for
external monitors.
3279 MIM
3.8 Base Logic Card (Location Dl)
The base logic card (see upper part of Figure 3-6)
contains:
The display buffer, which holds the character
code for each position on the screen.
The ROS which stores the character shapes. It
is addressed by the display buffer and the
outputs are fed to the Une control card.
• Attribute control circuits. The base attribute
byte defines the characteristics of the field.
Keyboard control circuits for keystrokes and
responses.
Logic for handling I/O operations with the.
display buffer. This involves the base I/O
address counter which is also used by the
features as an address for I/O operations.
• The character counters.
• Feature bus controls. The feature bus is the
main path for transmitting data around the
machine.
Chapter 3. Functional Components 3-9