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 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 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
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-210X/-211X/-250X 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
Character 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 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.
RST
1
CE
0
WR
0
0
1
1
RD
0
1
0
1
UNDEFINED
WRITE TO DISPLAY
READ FROM DISPLAY
UNDEFINED
CONTROL SIGNALS
FL
1
A
4
1
A
3
1
A
2
A
1
A
0
000 = LEFT MOST
111 = RIGHT MOST
CHARACTER
ADDRESS
CHARACTER RAM ADDRESS
D
7
0
1
D
6
D
5
D
4
D
3
D
2
D
1
D
0
128 ASCII CODE
X
X
X
UDC CODE
CHARACTER RAM DATA FORMAT
DIG
0
000
DIG
1
001
DIG
2
010
DIG
3
011
DIG
4
100
DIG
5
101
DIG
6
110
DIG
7
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.
11
AVAGO [ AVAGO TECHNOLOGIES LIMITED ]
