Understanding the DM74LS47N

[Valente]

the part that im working with is a bcd to seven segment converter and im writing a paper on it. the problem is i dont know what BI/RBO, RBI and LT are used for.
i kno what they stand for BI (Blanking input) RBO (Ripple Blanking output) RBI (Ripple Blanking Input) and LT (Lamp Test) but i dont know how these control pins work or what there supposed to do. so if anyone could help me out it would be greatly appreciated.

 

[jrz126]

got this from the datasheet

The SN54/74LS47 incorporates automatic leading and/or trailing-edge zero-blanking control (RBI and RBO). Lamp test (LT) may be performed at any time which the BI /RBO node is a HIGH level. This device also contains an overriding blanking input (BI) which can be used to control the lamp intensity by varying the frequency and duty cycle of the BI input signal or to inhibit the outputs.

here's the link to it **broken link removed**

 

[Valente]

thanks but i found that before and it dosent realy answer my question it just tells me what features the converter has

 

[Exo]

thanks but i found that before and it dosent realy answer my question it just tells me what features the converter has

Everything you want is in there!

LT is a lamp-test feature, active low. That means this line should be high for normal operation and, when pulled low, all 7-segments will be turned on so you can see all the 'lamps' are still good...

RBI is the ripple blanking input, also active low. It allows you to hide a '0'.
When this line is high, and there's a 0 at the inputs, a '0' will be displayed on the display. When the line is low with a 0 at the inputs, nothing will be displayed. This allows you to hide the leading zero's if, for example' you're displaying a short number on a large display.
(for example, 54 in stead of 00054)

BI/RBO is a wired-and pin, so it can be used as input and output, you should pull it high with a resistor, so the device can pull it low again.

BI is the blanking input, active low. It should be high for normal operation, when pulled low the display will be blank, regardless of whatever data is on the inputs.

When acting as output it becomes RB0 wich is the ripple blanking output. When you use RBI , and a '0' is on the inputs wich gets hidden, then this output becomes low, you can use it to inform the next lesser significant digit.

 

[Valente]

thank you so much. the stuff was there but i dident understand it, now i do.

 

[samcheetah]

i would recommend that you study the book Digital Fundamentals by Floyd. you will find alot of information about LED drivers encoders/decoders in that book. although the datasheet provides all the knowledge about a device it can be sometimes hard for a starter. for that u should have a good book with yourself. when u will have learnt the features of a couple of ICs u will be able to grasp all the info in datasheet very easily.