SM8580 datasheet(19/23 Pages) NPC

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SM8580AM

NIPPON PRECISION CIRCUITS—19

Digital Correction Registers (Bank 2, Registers 0, 1)

These registers enable and set the level of digital

correction applied to oscillator clock. DT_ON

enables the correction function, and bits DT0 to

DT6 set the level of correction to be applied. This

function adjusts the number of 1 second cycles

which occur every 10 seconds.

When digital correction is not used, a 0 should be

written to DT_ON to disable correction.

Correction range and resolution (correction range

depends on the frequency)

DT bits and digital correction (correction value

depends on the frequency)

Correction value calculation

• Positive correction (leading time)

[DT6:0] = correction ÷ 3.05 (with decimal

round-off)

Example: for correction of 192.15ppm

[DT6:0] = 192.15 ÷ 3.05 = 6310 = 01111112

• Negative correction (lagging time)

[DT6:0] = 128 + correction ÷ 3.05 (with deci-

mal round-off)

Example: for correction of

−158.6ppm

[DT6:0] = 128 + (

−158.6 ÷ 3.05) = 76

10 =

10011002

Bank

A d dress

Bit 3

Bit 2

Bit 1

Bit 0

Digital correction registers

DT3

DT2

DT1

DT0

DT_ON

D T 6

D T 5

D T 4

Correction range

Correction resolution

Correction cy cle

−195.20 to +192.15ppm

3.05ppm

10 seconds

Digital correction bits

Correction

(ppm)

DT6

DT5

DT4

DT3

DT2

DT1

DT0

0111111

+192.15

0111110

+189.10

↓↓

0000010

+6.10

0000001

+3.05

0000000

±0.00

1111111

−3.05

1111110

−6.10

↓↓

1000001

−192.15

1000000

−195.20

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