Help with temp. control fan hardware

hi all...
i was wondering how the "swap" command works in assembly and i couldnt find any info on it
for example if i have a number e.g. 05H and 0101B what would happen if i apply swap
is the answer 50H and 1100B ??
and i want to apply or logic to them lets say
0011 ORL 0110 and 50H ORL 04H

and also i wanted to know why some people connect pin 9 of 8051 in between a 1uF capacitor and 56k resistor...capacitor connected to 5V and resistor to GND ...all this instead of connecting to 5v with switch for reset ?

any response would be appreciated

swap command interchanges higher nibble with lower nibble.

i.e. if you swap 50H you will get 05H

regarding reset. well it is required to connect a capacitor and resistor to form an RC circuit and give a high to low pulse on reset pin. more information on selection of RC you can get in Intel 8051 user manual. visit download section to download it.

what if i want to apply or logic
0011 ORL 0110 and 50H ORL 04H
what would the answer be?
and why do we need high to low pulse on reset pin...cant we just replace it with reset push button with 5v?

0011 ORL 0110 => 0111

50H or 04H => 54H

regarding reset
read following..

hi... i was just wondering how do we select the frequency of the crystal that we used with uC why do we use 11.05.... and 12mhz and what would happen if we increase the size of the crystal... would the uC be faster???

yes controller will be faster. well choosing a crystal depends on type or project you are working on.. like if you want faster execution of code then u choose to increase speed, but sometimes you feel problem when you are trying to communicate between two controllers using uart and baud rate doesnt come perfect. i cant explain this coz its more of a practical issue than just conceptual one. :0

hi... i was wondering what are the benefits of using a M74HC04 hex inverter. i have tried to trigger a 12v 40mA fan by using just a TIP 31c power transistor...but didnt work i tried again with using both tip31 and hex inverter and it worked... what i have been told is that hex inverter can boost the current to the fan (current buffer) if this is true then isnt the power transistor suppose to do the same?? and why do we need power transistor?? and cant we used the normal one?

A tip31c should be able to drive a 40 mA fan without using a M74HC04.

It may be that the fan needs more than 40 mA, or your circuit is wrong.
Please post a diagram of your circuit.

I implemented the same project mentioned here.
But ZCD is not giving proper output. It should give 50 pulses per second. but it is giving approximately 35,000 pulse.
Has someone implemented the same project as mentioned here ?

Below is the ZCD diagram which I have implemented.

Please help me...

use this one..
http://www.8051projects.net/forum-t12385-post.html