| Symbol | Function |
| Cl C2 C3 C4 Rl R2 R3 R4 | Provides keyboard scanning . a. Keyboard scanning: HKS pin is LOW, the column group stays in "HIGH" stays and row group stays in "LOW" state. The key pad is compatible with the standard dual contact matrix keyboard (as Figure lb.), the inexpensive single contact keyboard (as Figure la.), and electronic input (as Figure lc.). When HKS is "low", a valid key entry is defined by related Row & Column connection or by electronic input; (as show in Figure lc). Activation of two or more keys will result in no response, except for single key. To avoid keyboard bouncing error, this chip provides built-in debounce circuit. (The debounce time = 20 ms.) - -l- - Row _AL Column - Figure la : Single contact form keyboard configuration L Row L Column Figure lb : Dual contact form keyboard configuration - -~D Row - - .VSS - -Y)D Co~umi-I_I _ _ - -' VSS Figure lc : Electronic signalinput keyboard configuration |
| OSCI OSCO | Oscillator input & Oscillator output pins. The 3.579545 MHz oscillator is formed by a built-in inverter inside of this chip and by connecting a 3.579545 MHz crystal or a ceramic resonator across the OSCI and OSCO pins. (built-in feedback resistor and capacitor) When HKS is "low", a valid key-in may turn on this oscillator and generates a 3.579545 MHz clock. |
| XMUTE | Mute output pins. NMOS open drain output structure. The output is in "low" state during dialing sequence (both Pulse and Tone mode) otherwise this pin is "high-impedance" . Long (continue) Mute. |
| VsS | Negative power supply pin. |
| VDD | Positive power supply pin. |
| HKS | Hook switch input pin. When the handset is in ON-HOOK state, this pin must be pulled "high" in order to disable the dialing operation and decrease the power consumption. When in OFF-HOOK state, the HKS pin must be pulled "low" state for all function operation. |
| PO | Pulse output signal pin. NMOS open drain output structure. The output is "low" during Dulse dialing and Flash operation, otherwise this output is "floating". |
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