HDSP-253X HP [Agilent(Hewlett-Packard)], HDSP-253X Datasheet - Page 12

• Manufacturer Part Number: HDSP-253X
• Description: Eight Character 5 mm Smart Alphanumeric Display
• Manufacturer: HP [Agilent(Hewlett-Packard)]

Self Test Function (Bits 5, 6)
Bit 6 of the Control Word Regis-
ter is used to initiate the self test
function. Results of the internal
self test are stored in bit 5 of the
Control Word. Bit 5 is a read only
bit where bit 5 = “1” indicates a
passed self test and bit 5 = “0”
indicates a failed self test.
Setting bit 6 to a logic 1 will start
the self test function. The built-in
self test function of the IC
consists of two internal routines
which exercises major portions of
the IC and illuminates all of the
LEDs. The first routine cycles the
ASCII decoder ROM through all
states and performs a checksum
on the output. If the checksum
agrees with the correct value, bit
5 is set to “1.” The second routine
provides a visual test of the LEDs
using the drive circuitry. This is
accomplished by writing
checkered and inverse checkered
patterns to the display. Each
pattern is displayed for approxi-
mately 2 seconds.
During the self test function the
display must not be accessed. The
time needed to execute the self
test function is calculated by
multiplying the clock period by
262,144. For example, assume a
clock frequency of 58 KHz, then
the time to execute the self test
function frequency is equal to
(262,144/58,000) = 4.5 second
duration.
At the end of the self test func-
tion, the Character RAM is loaded
with blanks, the Control Word
Register is set to zeros except for
bit 5, and the Flash RAM is
cleared and the UDC Address
Register is set to all ones.
Clear Function (Bit 7)
Bit 7 of the Control Word will
clear the Character RAM and the
Flash RAM. Setting bit 7 to a “1”
will start the clear function. Three
clock cycles (110 s min. using
the internal refresh clock) are
required to complete the clear
function. The display must not be
accessed while the display is
being cleared. When the clear
function has been completed, bit
7 will be reset to a “0.” The ASCII
character code for a space (20H)
will be loaded into the Character
RAM to blank the display and the
Flash RAM will be loaded with
“1”s. The UDC RAM, UDC
Address Register and the re-
mainder of the Control Word are
unaffected.
Display Reset
Figure 7 shows the logic levels
needed to reset the display. The
display should be reset on Power-
up. The external Reset clears the
Character RAM, Flash RAM,
Control Word and resets the
internal counters. After the rising
edge of the Reset signal, three
clock cycles (110 s min. using
the internal refresh clock) are
required to complete the reset
sequence. The display must not
be accessed while the display is
being reset. The ASCII Character
code for a space (20H) will be
loaded into the Character RAM to
Figure 7. Logic Levels to Reset the Display.
12
blank the display. The Flash RAM
and Control Word Register are
loaded with all "0"s. The UDC
RAM and UDC Address Register
are unaffected. All displays which
operate with the same clock
source must be simultaneously
reset to synchronize the Flashing
and Blinking functions.
Mechanical
Considerations
The HDSP-253X is assembled by
die attaching and wire bonding
280 LED chips and a CMOS IC to
a thermally conductive printed
circuit board. A polycarbonate
lens placed over the pcb creates
an air gap over the LED wire
bonds. A backfill epoxy seals the
display package.
Figure 8 shows the proper
method to insert the display by
hand. To prevent damage to the
LED wire bonds, apply pressure
uniformly with fingers located at
both ends of the part. Using a
tool, shown in Figure 9, such as a
screwdriver or pliers to push the
display into the printed circuit
board or socket may damage the
LED wire bonds. The force
exerted by a screwdriver is
sufficient to push the lens into the
LED wire bonds. The bent wire
bonds cause shorts or opens that
result in catastrophic failure of
the LEDs.