13
Figure 5. Logic Levels to Access the Flash RAM.
Control Word Register
Figure 6 shows how to access the
Control Word Register. This 8-bit
register performs five functions:
Brightness control, Flash RAM
control, Blinking, Self Test, and
Clear. Each function is
independent of the others; how-
ever, all bits are updated during
each Control Word write cycle.
Figure 6. Logic Levels to Access the Control Word
Register
Brightness (Bits 0-2)
Table 2. Current Requirements at
Bits 0-2 of the Control Word
adjust the brightness of the
display. Bits 0-2 are interpreted
as a three bit binary code with
code (000) corresponding to
maximum brightness and code
(111) corresponding to a blanked
display. In addition to varying the
display brightness, bits 0-2 also
vary the average value of IDD. IDD
can be calculated at any bright-
ness level by multiplying the
percent brightness level by the
value of IDD at the 100% bright-
ness level. These values of IDD are
shown in Table 2.
Different Brightness Levels VDD = 5.0 V
%
Current at 25°C
Symbol D2 D1 D0 Brightness
Typ.
Units
IDD (V)
0
0
0
0
1
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
100
80
53
40
27
20
13
200
160
106
80
mA
mA
mA
mA
mA
mA
mA
54
40
26
approximately 2 Hz. For an
external clock, the blink rate can
be calculated by driving the clock
frequency by 28,672. If the flash
enable bit of the Control Word is
a “0,” the content of the Flash
RAM is ignored. To use this
function with multiple display
systems, see the Display Reset
section.
eight digits of the display. When
this bit is a “1” all eight digits of
the display will blink at approxi-
mately 2 Hz. The actual rate is
dependent on the clock frequency.
For an external clock, the blink
rate can be calculated by dividing
the clock frequency by 28,672.
This function will override the
Flash function when it is active.
To use this function with multiple
display systems, see the Display
Reset section.
Flash Function (Bit 3)
Bit 3 determines whether the
flashing character attribute is on
or off. When bit 3 is a“1,” the
output of the Flash RAM is
checked. If the content of a loca-
tion in the Flash RAM is a “1,” the
associated digit will flash at
Blink Function (Bit 4)
Bit 4 of the Control Word is used
to synchronize blinking of all
HP [ HEWLETT-PACKARD ]
