HDSP-2131 Datasheet, PDF (11/16 Pages) Agilent(Hewlett-Packard) – Eight Character 5.0 mm (0.2 inch) Glass/Ceramic Intelligent 5 X 7 Alphanumeric Displays for Military Applications

Display Internal Block Diagram
Figure 1 shows the internal block
diagram of the HDSP-213x/-2179
display. The CMOS IC consists of
an 8 byte Character RAM, an 8
bit Flash RAM, a 128 character
ASCII decoder, a 16 character
UDC RAM, a UDC Address
Register, a Control Word
Register, and the refresh
circuitry necessary to synchron-
ize the decoding and driving of
eight 5 x 7 dot matrix
characters. The major user
accessible portions of the dis-
play are listed below:
Character RAM
Flash RAM
User-Defined Character RAM
(UDC RAM)
User-Defined Character
Address Register
(UDC Address Register)
Control Word Register
This RAM stores either ASCII character data or a UDC RAM address.
This is a 1 x 8 RAM which stores Flash data.
This RAM stores the dot pattern for custom characters.
This register is used to provide the address to the UDC RAM when the user is writing or
reading a custom character.
This register allows the user to adjust the display brightness, flash individual
characters, blink, self test, or clear the display.
Character Ram
Figure 2 shows the logic levels
needed to access the HDSP-213x/
-2179 Character RAM. During a
normal access the CE = “0” and
either RD = “0” or WR = “0”.
However, erroneous data may be
written into the Character RAM if
the Address lines are unstable
when CE = “0” regardless of the
logic levels of the RD or WR lines.
Address lines A₀-A₂ are used to
select the location in the Charac-
ter RAM. Two types of data can be
stored in each Character RAM
location: an ASCII code or a UDC
RAM address. Data bit D₇ is used
to differentiate between an ASCII
character and a UDC RAM
address. D₇ = 0 enables the ASCII
decoder and D₇ = 1 enables the
UDC RAM. D₀-D₆ are used to
input ASCII data and D₀-D₃ are
used to input a UDC address.
RST CE WR RD
0 0 UNDEFINED
1
0
0
1 WRITE TO DISPLAY
1 0 READ FROM DISPLAY
1 1 UNDEFINED
CONTROL SIGNALS
FL A₄ A₃ A₂ A₁ A₀
11 1
CHARACTER
ADDRESS
CHARACTER RAM ADDRESS
000 = LEFT MOST
111 = RIGHT MOST
D₇ D₆ D₅ D₄ D₃ D₂ D₁ D₀
0
128 ASCII CODE
1XXX
CHARACTER RAM DATA FORMAT
UDC CODE
DIG₀ DIG₁ DIG₂ DIG₃ DIG₄ DIG₅ DIG₆ DIG₇
000 001 010 011 100 101 110 111
SYMBOL IS ACCESSED IN LOCATION
SPECIFIED BY THE CHARACTER ADDRESS ABOVE
DISPLAY
0 = LOGIC 0; 1 = LOGIC 1; X = DO NOT CARE
Figure 2. Logic levels to access the character RAM.
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