On very many 8051's and 8052's of the older styles where the instruction cycle times are on the order of 1 uSec there just is not enough time between samples to calculate the next D/A converter values for SIN wave or DTMF generation. The time spent in software multiplies and divides will quickly eat up much of the bandwidth needed to keep a DTMF output updated.

It is not uncommon to use a D/A update rate on the order of 20 or 25 KHz to do SIN wave generation. That gives you 40 or 50 cycles per sample to get things done.

It is totally possible to generate DTMF on a the microcontroller. I have done it myself and have seen many examples on the web about others that have done it. And with a high enough sample rate it is possible to do the job with one lookup table!!!

Look also at these previous postings to this forum:

http://www.8052.com/forum/read.phtml?id=61031
http://www.8052.com/forum/read.phtml?id=49073
http://www.8052.com/forum/read.phtml?id=43306


Michael Karas