Datasheet

9
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-Dened Character RAM This RAM stores the dot pattern for custom characters.
(UDC RAM)
User-Dened Character This register is used to provide the address to the UDC RAM when
Address Register the user is 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.
Word Register and the refresh circuitry necessary to syn-
chronize the decoding and driving of eight 5 x 7 dot
matrix characters. The major user accessible portions of
the display are listed below:
Display Internal Block Diagram
Figure 1 shows the internal block diagram of the HDSP-
253X 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
Figure 2. Logic levels to access the character RAM.
Character Ram
Figure 2 shows the logic levels needed to access the HDSP-
253X 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 dierenti-
ate 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.
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
0 0
0 1
1
1 11
0
1 1
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