IBM 6580 User Manual

vides automatic cyclic redundancy
checks (CRC).
In a dual drive system, the software
instructs the diskette adapter card
microprocessor which diskette drive to
use.
DISPLAY ADAPTER CARD
This card is connected to the distrib-
ution board assembly in position D.
The display adapter card performs the
following functions:
• Receive data from the system
• Generate a character dot flow
• Supply the display with vertical
and horizontal signals
• Supply the display with RAM'data
The
system card microprocessor moves
data to the random access memory (RAM)
section of the display adapter card.
The RAM is a 4K byte memory that per-
forms a buffer function for the dis-
play. All data to be displayed is
held in the buffer (RAM) and formed
into a dot pattern. The dot pattern
is sent to the display in time with
the horizontal and vertical sweep
signals generated by this card. This
permits the character to be displayed
in the correct form and position
(Figure 6-7).
Microprocessor moves
Data
to be Displayed
to Display Adapter
Buffer
Dis;::>la
y Adapter Card
r-
-
I
Display
Buffer
I
(RAM)
Control Logic
and Character ....... - ...
Generator
L __ _
Figure 6-7. Display Data Flow
The
display adapter card supplies the
horizontal and vertical sweep signals
that move the beam left to right and
down the screen. These sweep signals
generate a magnetic field that guides
the beam to make a constant sweep pat-
tern.
Each dot of the pattern sent by the
display adapter makes a dot of light
on the display screen. The display
adapter keeps track of the beam while
it sweeps across the display screen.
When the beam is in the correct posi-
tion a data signal is sent from the
display adapter card, and a dot is
seen at the correct position. While
the sweep continues, more dots are
sent to complete each character to pe
displayed (Figure 6-8).
Because the complete screen is covered
by the sweep pattern approximately 35
times per second, the dots on the
screen seem to be on constantly.
6-8 IBM Displaywriter Product Support Manual

IBM 6580 Specifications

General

Brand	IBM
Model	6580
Category	Desktop
Language	English