Datasheet
11
eight 5 x 7 dot matrix
characters. The major user
accessible portions of the dis-
play are listed below:
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
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 A
0
-A
2
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 D
7
is used
to differentiate between an ASCII
character and a UDC RAM
address. D
7
= 0 enables the ASCII
decoder and D
7
= 1 enables the
UDC RAM. D
0
-D
6
are used to
input ASCII data and D
0
-D
3
are
used to input a UDC address.
Figure 2. Logic levels to access the character RAM.
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
Character RAM This RAM stores either ASCII character data or a UDC RAM address.
Flash RAM This is a 1 x 8 RAM which stores Flash data.
User-Defined Character RAM This RAM stores the dot pattern for custom characters.
(UDC RAM)
User-Defined Character This register is used to provide the address to the UDC RAM when the user is writing or
Address Register reading a custom character.
(UDC Address Register)
Control Word Register This register allows the user to adjust the display brightness, flash individual
characters, blink, self test, or clear the display.
CE
FL A
4
A
3
A
2
A
1
A
0
RST WR RD
CHARACTER
ADDRESS
SYMBOL IS ACCESSED IN LOCATION
SPECIFIED BY THE CHARACTER ADDRESS ABOVE
01
00
01
1
111
0
11
UNDEFINED
CONTROL SIGNALS
CHARACTER RAM ADDRESS
CHARACTER RAM DATA FORMAT
WRITE TO DISPLAY
READ FROM DISPLAY
UNDEFINED
000 = LEFT MOST
111 = RIGHT MOST
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
0 128 ASCII CODE
X X X UDC CODE1
DISPLAY
0 = LOGIC 0; 1 = LOGIC 1; X = DO NOT CARE
DIG
0
DIG
1
DIG
2
DIG
3
DIG
4
DIG
5
DIG
6
DIG
7
001 010 011 100 101 110 111000