SI3233 datasheet(22/100 Pages) SILABS

22 / 100 page

Si3233

Preliminary Rev. 0.5

Figure 9. Loop Closure Detection

2.2.6. Loop Closure Detection

A loop closure event signals that the terminal equipment

has gone off-hook during on-hook transmission or on-

hook active states. The ProSLIC performs loop closure

detection digitally using its on-chip monitor A/D

converter. The functional blocks required to implement

loop closure detection are shown in Figure 9. The

primary input to the system is the Loop Current Sense

value provided in the LCS register (direct Register 79).

The LCS value is processed in the Input Signal

Processor when the ProSLIC is in the on-hook

transmission or on-hook active linefeed state, as

indicated by the Linefeed Shadow register, LFS[2:0]

(direct Register 64). The data then feeds into a

programmable digital low-pass filter, which removes

unwanted ac signal components before threshold

detection.

The output of the low-pass filter is compared to a

programmable threshold, LCRT (indirect register 15).

The threshold comparator output feeds a programmable

debouncing filter. The output of the debouncing filter

remains in its present state unless the input remains in

the opposite state for the entire period of time

programmed by the loop closure debounce interval,

LCDI (direct Register 69). If the debounce interval has

been satisfied, the LCR bit will be set to indicate that a

valid loop closure has occurred. A loop closure interrupt

is generated if enabled by the LCIE bit (direct

written or monitored to correctly detect a loop closure

condition.

2.2.7. Loop Closure Threshold Hysteresis

Programmable hysteresis to the loop closure threshold

can be enabled by setting HYSTEN = 1 (direct

(indirect Register 15) and LCRTL (indirect Register 66),

which set the upper and lower bounds, respectively.

Power Alarm Interrupt Enable

Bits 2 to 7 corre-

spond to Q1 to Q6,

respectively

N/A

QnAE[n+1],

where n = 1 to 6

Direct Register 22

Power Alarm

Automatic/Manual Detect

0 = manual mode

1 = enter open state

upon power alarm

N/A

AOPN

Direct Register 67

*Note:

The ProSLIC uses registers that are both directly and indirectly mapped. A “direct” register is one that is mapped

directly. An “indirect” register is one that is accessed using the indirect access registers (direct registers 28 through

31).

Table 22. Associated Power Monitoring and Power Fault Registers (Continued)

ISP_OUT

NCLR

LCDI

Input

Signal

Processor

Digital

LPF

Loop Closure

Threshold

Debounce

Filter

–

LCR

LCIP

LCIE

Interrupt

Logic

LCS

LVS

LCVE

LFS

LCRTL

LCRT

HYSTEN

SI3233 Datasheet(PDF) 22 Page - Silicon Laboratories

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