Silicon Laboratories SI2493/57/34/15/04 manual Pdl, Line-Side Chip Power Down, = Normal operation

AN93

			Table 65. U65 Bit Map (Continued)
12:7	Reserved	Read returns zero.
6:5	Reserved	Do not change (use read-modify-write).
4	PDL	Line-Side Chip Power Down.
		0	= Normal operation.
		1	= Places the Si3018/10 in Power-Down mode.
3:2	Reserved	Read returns zero.
1:0	Reserved	Do not change (use read-modify-write).

U66 (DAAC5) is a bit-mapped register with all bits except bit 6 reserved (see Table 66).

Bit 6 (FDT) is a read-only bit that reports whether or not an isolation capacitor frame lock is established. FDT is typically used for board-level debugging and is not used during normal modem operation.

U66 resets to 0xXX40 with a power-on or manual reset assuming framelock is established. The upper byte is variable.

5.7.17. U67–U6A (International Configuration Registers)

International Configuration Registers include U67 through U6A. These are bit-mapped registers that control international configuration settings, such as dc and ac termination, ringer impedance and detection, current limit, and billing tone protection.

U67 is a bit-mapped register with bits 5:4, 8, 11:10, and 15:14 reserved (see Table 67). U67 resets to 0x0008 with a power-on or manual reset.

Bit 7 (DCR) is used to set the dc line termination of the modem. DCR = 0 is the normal mode of operation with dc impedance selected by U67 [3:2] (DCV).

When DCR = 1, the device presents a dc line impedance of 800 Ω, which can be used to enhance operation with a parallel phone, for improved low line voltage performance, and for overload. This bit must be set to 0 when the modem is on-hook.See "6.2.1. DC Termination" on page 133 for details.

Bit 6 (OHS) is used to control the speed with which the modem drops the line. The default setting, OHS = 0, causes the modem to go from the off-hook state (drawing loop current) to the on-hook state (not drawing loop current) quickly. This operation is acceptable in many countries. However, some countries, such as Italy, South Africa, and Australia, have spark quenching requirements. Spark quenching can be accomplished by placing a resistor and a capacitor across the hookswitch or by controlling the off-hook to on-hook transition speed to prevent excessive voltage buildup. Slowly reducing the loop current to zero fulfills the spark quenching requirement without the extra components. Setting OHS = 1 causes the hookswitch to turn off the loop current with a ramp instead of a step.

Bits 3:2 (DCV) select the dc termination for the modem. DCV = 00 is the lowest voltage mode supported on the ISOmodem. DCV = 01 is the next lowest voltage mode. See "6.2.1. DC Termination" on page 133 for details.

Bit 1 (RZ) = 0 (default) allows ringer impedance to be determined by external components. This impedance is typically 800–900 kΩ. RZ = 1 enables on-chip synthesis of a lower ringer impedance for countries, such as Poland, South Africa, and South Korea.

Bit 0 (RT), Ring Threshold, is used to satisfy various country ring detect requirements. RT = 0 (default) sets the ring threshold for 11–22 VRMS. RT = 1 sets the ring threshold for 17–33 VRMS. Signals below the lower level of the range are not detected. Signals above the upper level of the range are always detected.

108 Rev. 1.3