Maxim-integrated 73M1866B/73M1966B Implementers Guide Uživatelský manuál stáhnout pdf (Strana 13)

UG_1x66B_016 73M1866B/73M1966B Implementer’s Guide

Rev. 1.3 13

3.2.2 Receiver DC Offset Calibration

The effect of residual DC offset caused by the external components to the 73M1x66B can be reduced by

a simple procedure in which the magnitude of this DC offset is measured and subtracted from each

sample received from the PSTN. This calibration is intended to be performed once after power-on/reset

and is done only after the PLL is locked and the barrier is synchronized. The calibration can be

performed later if circumstances require intermittent calibration (for example if operating temperatures

vary drastically). The procedure can only be performed when the device is On-Hook.

The registers used in this procedure are:

0x12

OFH

ENDC

ENAC

ENSHL

ENLVD

ENFEL

ENDT

ENNOM

Write

0 0 1 X 0 1 0 X

0x15

ENOLD

DISNTR

Res

CIDM

THEN

ENUVD

ENOVD

ENOID

Write

X X X X 1 0 X X

0x16

TXEN

RXEN

RLPEN

ATEN

ACZ3

ACZ2

ACZ1

ACZ0

Write

0 X X 0 X X X X

0x17

Res

RXOCEN

Res

Write

X X 1/0 X X X X X

0x25

RXOM7

RXOM6

RXOM5

RXOM4

RXOM3

RXOM2

RXOM1

RXOM0

Read/

Write

OFFSET

The temporary variables defined in this procedure are:

OFFSET = DC Offset value, RXOM[7:0].

Begin

1. Ensure that the device is On Hook (OFH==0). Executing the procedure when Off Hook will degrade

performance. If the device is Off Hook, return an error code indicating that the device cannot perform

the calibration routine.

2. Set ENDC, ENLVD and ENDT to 0; set ENAC and ENFEL to 1 (write RG12 = x01x_010x2).

3. Set THEN to 1 and ENUVD to 0 (write RG15 = xxxx_10xx).

4. Set TXEN and ATEN to 0 (write RG16 = 0xx0_xxxx).

5. Set RXOCEN to 1 (write RG17 = xx1x_xxx).

6. Allow 1 second for the receive offset measurement to stabilize.

7. Set RXOCEN to 0 (write RG17 = xx0x_xxxx).

8. OFFSET = RXOM[7:0] (Read RG25).

9. Add 08h to OFFSET and write this result back into RXOM[7:0] (RG25 = OFFSET).

End

0x14 TXBST DAA1 DAA0 Res RXBST RLPNH RXG1 RXG0

Write X X X 0 X X X X

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 28 29

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