SA545

`The circuit in Figure 7 uses a constant current supply to draw current from the telephone line which is used to power the SA54X5. The 2,5V reference 
  diodeproduces a stabilised supply voltage which determines the DTMF tone level of the SA545.
`In Figure 8, a stabilising voltage from the speech circuit is used to supply the SA545 during DTMF dialling to give accurate tone levels.
`The SA545 is powered via the 150KW resistor during TBR operations and LD dialling breaks, and via T1 during dialling makes. This configuration
   minimises the component count, at the expense of allowing a leakage current of about 450A during dialling breaks. The 47F reservoir
   capacitor maintains   and smoothes the supply to the chip.

The SAMES SA545 is a family of keypad switchable Loop Disconnect (LD)/Dual Tone multi-Frequency (DTMF) dialler devices for use in low-cost, dual dialling mode telephone instruments.

The SAMES SA545 feature automatic storage of a single telephone number of up to 24 digits for Last Number Redial (LNR) purposes as well as10 repertory dialling memories capable of each storing 24 digits. The low current consumption of the SA545 ensures memory retention while powered from the line.

Two modes of operation are available. The first is a LD/DTMF mode which operates normally in LD mode, but can be switched temporarily via the keypad to DTMF mode during a call. SAMES SA545 has been optimised for applications such as home banking, credit-card verification and other applications requiring low speed data communications. The second mode allows DTMF dialling only.

The Lock function of SAMES SA545 will be described in the Functional Description.