SA541

`The circuit in Figure 7 uses a constant current supply to draw current from the telephone line which is used to power the SA54X1. The 2,5V reference
   diode produces a stabilised supply voltage which determines the DTMF tone level of the SA54X1.

`In Figure 8, a stabilising voltage from the speech circuit is used to supply the SA54X1 during DTMF dialling to give accurate tone levels.

`The SA54X1 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 SA54X1 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 SA54X1 feature automatic storage of a single telephone number of up to 32 digits for Last Number Redial (LNR) purposes. The low current consumption of the SA54X1 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. This mode is intended 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 SA54X1 will be described in the Functional Description. The SA54X1 is pin compatible with SAMES' SA54X5 family of diallers.