Clock operation

M41T256Y

20/30

second either shortened by 128 or lengthened by 256 oscillator cycles. If a binary '1' is

loaded into the register, only the first 2 minutes in the 64 minute cycle will be modified; if a

binary 6 is loaded, the first 12 will be affected, and so on.

Therefore, each calibration step has the effect of adding 512 or subtracting 256 oscillator

cycles for every 125,829,120 actual oscillator cycles, that is +4.068 or –2.034 ppm of

adjustment per calibration step in the calibration register. Assuming that the oscillator is

running at exactly 32,768Hz, each of the 31 increments in the calibration byte would

represent +10.7 or –5.35 seconds per month which corresponds to a total range of +5.5 or –

2.75 minutes per month.

Figure 11.

Crystal accuracy across temperature

Figure 12.

Clock calibration

Two methods are available for ascertaining how much calibration a given M41T256Y may

require.

AI00999b

–160

0

10203040506070

Frequency (ppm)

Temperature

°C

80

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

20

0

–20

ΔF

2

K = –0.036 ppm/

F

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION