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National Semiconductor - Graphics/Alphanumerics Systems Using the DP8350

Numéro de référence AN-243
Description Graphics/Alphanumerics Systems Using the DP8350
Fabricant National Semiconductor 
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AN-243 fiche technique
Graphics Alphanumerics
Systems Using the DP8350
National Semiconductor
Application Note 243
Mike Evans
July 1986
This Application Note summarizes some CRT terminal cir-
cuits each with an increasing degree of graphics capability
and then goes into detail to describe a system having full
graphics capability with all dots individually programmable
All these applications use the DP8350 CRT Controller
Here are some of the features of the full graphics system
Hardware Features
 The hardware is designed for a 24 row by 80 column
display with 7 dots per column and 10 lines per row
 All ICs are made by National Semiconductor
 Low I C cost all parts readily available
 Fits on one standard BLC80 (SBC80) card
 System performance only limited by software
 8080 Mnemonics usable with STARPLEXTM or Intel-
lec Development Systems
 All graphics programs very fast
Example One dot takes 500 ms maximum to plot
 During display time each 7-dot cycle may be shared by
the microprocessor
 8-bit word comprises MSB as attribute and next 7 bits as
7 dot word of a character line
 Can input display data serially or parallel
 Can output display data serially or parallel
 Baud rate programmable from 110 to 56k baud
 Can be used as slave to main system
 Can copy characters from alphanumeric ROM or symbol
EPROM
 13 kbytes of RAM available for user software or back-up
display storage
 Analog inputs joystick or waveforms
 Easily expandable to color graphics
Software Features
 The software is programmed for any display configura-
tion of rows columns dots per column and lines per row
The hardware is designed for a 24 row by 80 column
display with 7 dots per column and 10 lines per row
 Can perform most dumb terminal functions including
scrolling
 Simultaneous display of alphanumerics and graphics
 Identical terminals can display same information with in-
puts from either
 Can save displays in computer storage
 Can load displays from computer storage
 Can erase any part of display or all of it
 Can draw a rectangle linking any 2 horizontal and 2 verti-
cal coordinates
 Can transfer in 1 10th second max any area of display to
any other area or to from backup display storage
 Smooth movement of subject in any direction
 Immediate display of fixed diagrams
 In-system emulation of programs available
The DP8350 CRT Controller provides incrementing video
addresses starting from the Top of Page address or from a
new Row Start address These addresses and the Cursor
address are loaded into their respective registers from the
address bus All video control signals are provided by the
8350 so that apart from the crystal oscillator no extra video
circuitry is required
The DP8350 has so far been considered to be useable only
in dumb terminals whereas in fact it is easy to adapt it to
more complex terminals with full graphics capability Follow-
ing is a summary of the functions of the various combina-
tions of alphanumerics graphics displays beginning with a
dumb terminal using a monitor with 24 x 80 characters
Dumb Terminal
The basic dumb terminal design is shown in Figure 1 Usual-
ly the microprocessor loads the Character Position RAM (or
Refresh RAM) only during horizontal or vertical blanking or
during the last 3 lines of a row The CRTC then sequentially
addresses this RAM during display time The ASCII data
from this RAM (for the character selected) is outputted to
the ROM of the Character Generator The 7-dot word of this
character for the line being displayed is then loaded into a
shift register and shifted out as video to the monitor during
the next 7-dot cycle
The logical choice of CRT Controller for this simple CRT
terminal is the DP8350 The most common application is for
a 24 row by 80 column display with the character field com-
prised of 10 lines each of 7 dots The character itself occu-
pies 7 lines each of 5 dots leaving 3 lines for vertical char-
acter spacing and 2 dots for horizontal character spacing
Refer to AN-198 and AN-199 for further information on al-
phanumeric applications of CRTs
STARPLEXTM is a trademark of National Semiconductor Corp
Intellec is a registered trademark of Intel Corp
C1995 National Semiconductor Corporation TL F 5868
RRD-B30M105 Printed in U S A
Free Datasheet http://www.0PDF.com

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