Datasheet
11
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-Dened Character RAM This RAM stores the dot pattern for custom characters.
(UDC RAM)
User-Dened Character This register is used to provide the address to the UDC RAM when the user is
Address Register writing or reading a custom character.
(UDC Address Register)
Control Word Register This register allows the user to adjust the display brightness, ash individual
characters, blink, self test, or clear the display.
Display Internal Block Diagram
Figure 1 shows the internal block diagram of the HDSP-
210X/-211X/-250X displays. The CMOS IC consists of an 8
byte Charac ter 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 refresh circuitry
necessary to synchronize the decoding and driving of
eight 5 x 7 dot matrix characters. The major user-acces-
sible portions of the display are listed below:
Character RAM
Figure 2 shows the logic levels needed to access the
HDSP-210X/-211X/-250X Character RAM. During a
normal access, the CE = “0” and either RD = “0” or WR =
“0.” However, erro neous 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
Char ac 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 dierentiate between the
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.
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