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-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

Address Register

writing or 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.

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

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.

Character RAM. Two types of data can be stored in each

Character RAM location: an ASCII code or a UDC RAM

input a UDC address.

Figure 2. Logic levels to access the character RAM.

CE

FL

RST

WR

RD

CHARACTER

ADDRESS

SYMBOL IS ACCESSED IN LOCATION

SPECIFIED BY THE CHARACTER ADDRESS ABOVE

0

1

0

0

0

1

1

1

1

1

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

0

128 ASCII CODE

X

X

X

UDC CODE

1

DISPLAY

0 = LOGIC 0; 1 = LOGIC 1; X = DO NOT CARE

001

010

011

100

101

110

111

000