Features: 89E516RD Microcontroller based stored program control having Memory of 72KB Program memory & 1KB Data RAM memory. No. of Subscribers Two DOT Lines, Four Extension Lines Line Section are Opto Isolated for Trunk Lines and 4 Extension Lines. Tone Generation like Dial Tone, Busy Tone,Ring Back Tone, Hold-on music etc. Speech Path is Fully Non- Blocking. Switch Faults : 8 Switch Faults are provided on board to study different effects on circuit.