about 4 bit counter and R-2R...?

[jm1]

we were given a proj to our own basic voltmeter.. it is composed maninly of a 4 bit counter, a r-2r, and an op amp.. my question are.. what is a R-2R? what does a 4 bit counter do?what is the difference between synchronous and asynchronous 4 bit counters?

 

[Rasta_Man]

4-Bit Counter

just learnt a bit about 4-bit Counters at school it is made up of d-type flip-flops. it counts in binary from 0000 to 1111

**broken link removed**

here it what is looks like. the clock bar makes the 4-bit counter change on the falling edge of the clock pulse. that is about all i know about them at the moment sorry if it didnt realy answer your question about them, i have no idea about the others