7

Electrical Description

Pin Function

Description

Clear (CLR, pin 3)

When CLR is a logic 0 the ASCII RAM is reset to 20hex (space) and the Control

Register/Attribute RAM is reset to 00hex.

Cursor Enable

CUE determines whether the IC displays the ASCII or

(CUE pin 4)

the Cursor memory. (1 = Cursor, 0 = ASCII).

Cursor Select

CU determines whether data is stored in the ASCII RAM

(CU, pin 5)

or the Attribute RAM/Control Register. (1 = ASCII, 0 = Attribute RAM/Control Register).

Write (WR, pin 6)

WR must be a logic 0 to store data in the display.

Address Inputs

Address 00 accesses the far right display location.

Pins 8 and 7)

Address 11 accesses the far left location.

Data Inputs

display.

GND (pin 10)

GND is the display ground.

Blanking Input

BL is used to flash the display, blank the

(BL, pin 18)

display or to dim the display.

Display Internal Block Diagram

Figure 1 shows the HDLX-2416 display internal block

diagram. The CMOS IC consists of a 4 x 7 Character

RAM, a 2 x 4 Attribute RAM, a 5 bit Control Register, a

128 character ASCII decoder and the refresh circuitry

necessary to synchronize the decoding and driving of

four 5 x 7 dot matrix displays.

Four 7 bit ASCII words are stored in the Character RAM.

The IC reads the ASCII data and decodes it via the 128

character ASCII decoder. The ASCII decoder includes the

64 character set of the HPDL-2416, 32 lower case ASCII

symbols, and 32 foreign language symbols.

A 5 bit word is stored in the Control Register. Three fields

within the Control Register provide an 8 level brightness

control, master blank, and extended functions disable.

For each display digit location, two bits are stored in

the Attribute RAM. One bit is used to enable a cursor

character at each digit location. A second bit is used to

individually disable the blanking features at each digit

location.

The display is blanked and dimmed through an internal

blanking input on the row drivers. Logic within the IC

allows the user to dim the display either through the BL

input or through the brightness control in the control

register. Similarly the display can be blanked through the

BL input, the Master Blank in the Control Register, or the

Digit Blank Disable in the Attribute RAM.