After detecting presence of a valid DTMF signal StD goes high for Short duration (Refer Data sheet) and outputs Q1-Q4 gets latched according to received tone-pair (Refer above table) ALGORITHM · Poll for Ring Detection. · Activate of relay to place 220 Ohm (1/2 watt.) resistor in line so as to lift phone .(The 220-ohm loop on telephone line disconnects the ringer from the telephone line in the exchange.) · Poll for StD and when it goes high Read port 0 to find out received tone-pair from Q1-Q4. · Take control action according to received tone & Poll for the strobe again if you wish and deactivate relay when you finish. COADING (ASSEMBLY LANGUAGE) ·...
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