Datasheet

13
Figure 5. Logic levels to access the ash RAM.
Table 2. Current Requirements at Dierent Brightness Levels V
DD
= 5.0 V
% Current at 25°C
Symbol D
2
D
1
D
0
Brightness Typ. Units
I
DD
(V) 0 0 0 100 200 mA
0 0 1 80 160 mA
0 1 0 53 106 mA
0 1 1 40 80 mA
1 0 0 27 54 mA
1 0 1 20 40 mA
1 1 0 13 26 mA
Figure 6. Logic levels to access the control word register
Control Word Register
Figure 6 shows how to access the Control Word Register.
This 8-bit register performs ve functions: Bright ness
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.
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 calcu lated at any
bright ness level by multiplying the percent brightness
level by the value of I
DD
at the 100% bright ness level.
These values of I
DD
are shown in Table 2.
Flash Function (Bit 3)
Bit 3 determines whether the ashing character attribute
is on or o. 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 ash at approximately 2 Hz.
For an external clock, the blink rate can be calculated by
driving the clock frequency by 28,672. If the ash enable
bit of the Control Word is a “0,” the content of the Flash
RAM is ignored. To use this function with multiple dis play
systems, see the Display 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 approx i mately 2
Hz. The actual rate is dependent on the clock fre quency.
For an external clock, the blink rate can be calculated by
dividing the clock frequency by 28,672. This func tion will
override the Flash function when it is active. To use this
function with multiple display systems, see the Display
Reset section.
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
0 0 0 100%
00180%
01053%
01140%
10027%
10120%
11013%
1110%
BB