Datasheet

13
Control Word Register
Figure 6 shows how to access the
Control Word Register. This is an
eight bit register which performs
five functions. They are Bright-
ness control, Flash RAM control,
Blinking, Self Test and Clear.
Each function is independent of
the others. However, all bits are
updated during each Control
Word write cycle.
Brightness (Bits 0-2)
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 I
DD
. I
DD
can be calculated at any bright-
ness level by multiplying the
percent bright-ness level by the
value of I
DD
at the 100%
brightness level. These values of
I
DD
are shown in Table 2.
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
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 Reset section.
Blink Function (Bit 4)
Bit 4 of the Control Word is used
to synchronize blinking of all 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 Reset
section.
Figure 5. Logic levels to access the flash RAM.
Figure 6. Logic levels to access the control word register.
Table 2. Current Requirements at Different Brightness Levels
Symbol D
2
D
1
D
0
% Brightness 25°C Typ. Units
I
DD
(V) 0 0 0 100 200 mA
00180 160 mA
01053 106 mA
01140 80 mA
10027 54 mA
10120 40 mA
11013 26 mA
CE
FL A
4
A
3
A
2
A
1
A
0
RST WR RD
01
00
01
1
XX0
0
11
UNDEFINED
REMOVE FLASH AT
SPECIFIED DIGIT LOCATION
STORE FLASH AT
SPECIFIED DIGIT LOCATION
CONTROL SIGNALS
FLASH RAM ADDRESS
FLASH RAM DATA FORMAT
0 = LOGIC 0; 1 = LOGIC 1; X = DO NOT CARE
WRITE TO DISPLAY
READ FROM DISPLAY
UNDEFINED
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
X
XXXXXX
0
1
CHARACTER
ADDRESS
000 = LEFT MOST
111 = RIGHT MOST
CE
FL A
4
A
3
A
2
A
1
A
0
RST WR RD
01
00
01
1
10XXX1
0
11
UNDEFINED
CONTROL SIGNALS
CONTROL WORD ADDRESS
CONTROL WORD DATA FORMAT
0 = LOGIC 0; 1 = LOGIC 1; X = DO NOT CARE
0 DISABLE FLASH
1 ENABLE FLASH
BRIGHTNESS
CONTROL
LEVELS
0 DISABLE BLINKING
1 ENABLE BLINKING
0 NORMAL OPERATION
1 CLEAR FLASH AND CHARACTER RAMS
0 X NORMAL OPERATION; X IS IGNORED
1 X START SELF TEST; RESULT GIVEN IN X
X = 0 FAILED X = 1 PASSED
WRITE TO DISPLAY
READ FROM DISPLAY
UNDEFINED
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
C
SSBLFB
000100%
00180%
01053%
01140%
10027%
10120%
11013%
1110%
BB