HDSP-2533 Datasheet, PDF (9/15 Pages) AVAGO TECHNOLOGIES LIMITED – Eight Character 5 mm Smart Alphanumeric Display

Display Internal Block Diagram
Figure 1 shows the internal blockdiagram 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
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:
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-
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 A₀-A₂ 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 D₇ is used to differenti-
ate between the 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
0
1
0
0
1
1
CONTROL SIGNALS
RD
0 UNDEFINED
1 WRITE TO DISPLAY
0 READ FROM DISPLAY
1 UNDEFINED
FL A4 A3 A2 A1 A0
1
1
1
CHARACTER
ADDRESS
CHARACTER RAM ADDRESS
000 = LEFT MOST
111 = RIGHT MOST
D7
D6
D5
D4
D3
D2
D1
D0
0
128 ASCII CODE
1
X
X
X
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.