What's the meaning of overflow, borrow bit and carry bit?

[ilop]

help

hello

i want to ask some questions, here are:
1. what's the meaning of overflow, borrow bit and carry bit
2. i want to make a circuit that if we press 1 or 2 or 3 in keypad, there will be an output in seven segment(the output is 2 bit) i want to ask where can i find the circuit in internet?i have searched in google but i didn't find anything

thank

 

[IanP]

Re: help

Use this link to find explenations on carry, borrow and overflow:
**broken link removed**

Re. your circuit: Do you want to generate 00(key1), 01(key2) and 10(key3) ?

 

[ilop]

Re: help

yes i want to generate it to 7 segment, but not only 1,2,3 but also 5 to 9, and it can generate 4 bits like 1234 etc, how???

i am asked to make that using GAL 16v8, i am forbidden to use another decoder, except keypad decoder..so i must to make the program about generating numeric to 7 segment... can you help???

 

[IanP]

Re: help

Check what code is output from your keypad. Quite possible you will have just simple BINARY or BCD and in both cases it means that fror keys 0 to 9 you have the same code: key 0 = 0000, key 1 = 0001, ..key9=1001. So you have 4 inputs to your GAL. To display the result on seven segment diplay you will have 7 outputs and the only thing to create is to write TRUTH TABLE. How to do it you can find in the following example but it converts BCD to GRAY Code so .. you will have to create your own table ..
**broken link removed**

 

[ilop]

Re: help

hello... thank you for the advice.i want to ask, what do you mean by the output is 7? does it mean 7 bits?.. if so there is only one digit of numeric?

i want to make a keypad that can generate 3 digits from keypad to 7 segment so if i press 1 in the keypad then the 7 segment generate numeric 1, if i press 1 2 3 4, it generates 1234 and soon.. so there will be 7x4 bits, am right?if so.. to do that there will be a shift-register..

d'oh i am confused... do you have that schematic that can make that keypad

 

[IanP]

Re: help

In your previous post you mentioned GAL16V8.
Do you still have to use it?
Its application can be conversion from input buttons 1, 2, 3,...9 to their 7-segment codes and then using modulo-7 counter shift them into 28-bit shift register and display this 28-bit register as 4 x 7-segmant.

Can you use a small microcontroller?
Would be quite easy to implement your project in one microcontroller ..

 

[ilop]

Re: help

hello

yes i still use the GAL 16V8, because my lecturer asks me to use that not other, i can't use microcontroller, i am confused about the program in gal 16v8 that can make that 28 shift register. can you help?