I have been doing experiments on few of the pbx avaiable in local market specially those which use At89c52 and MT8816. Now iam having a problem in making the controller detect off-hook.
I want the controller to sent the dial-tone when ever the telephone goes off-hook, using my mutlimeter i found that when the telephone goes off-hook meter shows 5 volts on controller bit where the off-hook is connected so its means it is active high.
so just to do experiment no professional work i used the command
JNB p2.0,$ ;waiting for off-hook
dial tone data
now the above should work in such a way taht when the telephone goes off-hook controller should sent data to mt8816 to sent dial tone to the telephone but its not working instead if i only write the program in such a way that when where the pbx turn on controller should sent dial tone it works but this is not the right way controller should only sent dial tone when the telephone goes off-hook .. i haev used the JB p2.0,$ command to check it the controller detects off hook as a low signal but its not correct also..
so is there any way which iam missing in order to detect the off-hook on this pbx like debouncing etc..