MC3401A/3411A
LED Display
MC3401A/3411A provides 4 LED Display Terminals, namely LED1 to LED4. Data is written to the LED Port starting
from the least significant bit (b0) of the port using a WRITE Command. Each bit starting from the least significant
(b0) activates a specific LED Display Terminal – b0 corresponds LED1 Display, b1 activates LED2 and so forth.
Since there are only 4 LED display terminals, bits 5 to 8 (b4 ~ b7) are not used and therefore ignored. This means
that b4 to b7 does NOT in anyway activate any LED Display, they are totally ignored.
When a bit (b0 ~ b3) in the LED Port is “1”, the corresponding LED is OFF. Conversely, when the bit is “0”, the LED
Display is turned ON. For example, Bit 1 (as designated by b0) has the value of “1”, then this means that LED1 is
OFF. It must be noted that when power is turned ON, bit 1 to bit 4 (b0 to b3) are given the value of “0” (all
LEDs are turned ON). Please refer to the diagrams below.
MSB
LSB
-
-
-
-
b3 b2 b1 b0
Don’t Care
LED1
LED2
LED3
LED4
February 28, 2013 Ver. 1.10
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