Wang 5536 - Functional Description; Pca

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2.3 FUNCTIONAL DESCRIPTION
This section provides descriptions of all workstation logic functions.
2.3.1 210-7545-2 PCA
The 7545 PCA contains VIDEO DISPLAY LOGIC, CRT MEMORY, KEYBOARD INTERFACE
and Z80A CPU, and these related logic functions:
o IN-OUT decoders
o Parity generation and check (even parity)
o Memory configuration (DIP switches)
o Audio prompt (beep/click)
2.3.1.1 Video Display Logic (Figure 2-2)
The 5536 workstations display 1920 character locations arranged in 24 rows
of 80 characters or columns. Each character on the screen has a unique
memory-address containing the code of the character being dis played. The
number of characters per row may be extended to 158 to accommodate the
extended columns used by wide-platen printers and line printers. These
additional 1872 character spaces (total 3792) are also accommodated in CRT
memory; however, only 80 columns can be displayed at one time. The
additional row length can only be observed by performing a horizontal
scroll (Optional-WP, Standard-DIS) •
An additional four-bit control field is associated with each CRT address.
This control field permit~ each character to be blinked, intensified,
underlined, and/or accompanied by a cursor. Separate parity bits accompany
each character and each control field to ensure data integrity.
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Figure 2-2. Video Display and Control Block Diagram
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