ISL12025 Datasheet, PDF (12/27 Pages) Intersil Corporation – Real-Time Clock/Calendar with I2C Bus and EEPROM

ISL12025
Alarm Registers (Non-Volatile)
Alarm0 and Alarm1
The alarm register bytes are set up identical to the RTC
register bytes, except that the MSB of each byte functions as
an enable bit (enable = “1”). These enable bits specify which
alarm registers (seconds, minutes, etc.) are used to make
the comparison. Note that there is no alarm byte for year.
The alarm function works as a comparison between the
alarm registers and the RTC registers. As the RTC
advances, the alarm will be triggered once a match occurs
between the alarm registers and the RTC registers. Any one
alarm register, multiple registers, or all registers can be
enabled for a match. See “Device Operation” on page 13
and “Application Section” on page 21 for more information.
Control Registers (Non-Volatile)
The Control Bits and Registers described in the following are
non-volatile.
BL Register
BP2, BP1, BP0 - Block Protect Bits
The Block Protect Bits, BP2, BP1 and BP0, determine which
blocks of the array are write protected. A write to a protected
block of memory is ignored. The block protect bits will
prevent write operations to one of eight segments of the
array. The partitions are described in Table 3.
TABLE 3.
PROTECTED ADDRESSES
ISL12025
ARRAY LOCK
000
None (Default)
None
001
010
011
100
101
110
111
180_h – 1FF_h
100_h – 1FF_h
000_h – 1FF_h
000_h – 03F_h
000_h – 07F_h
000_h – 0FF_h
000_h – 1FF_h
Upper 1/4
Upper 1/2
Full Array
First 4 Pages
First 8 Pages
First 16 Pages
Full Array
Oscillator Compensation Registers
There are two trimming options.
- ATR. Analog Trimming Register
- DTR. Digital Trimming Register
These registers are non-volatile. The combination of analog
and digital trimming can give up to -64ppm to +110ppm of
total adjustment.
ATR Register - ATR5, ATR4, ATR3, ATR2, ATR1,
ATR0: Analog Trimming Register
Six analog trimming bits, ATR0 to ATR5, are provided in
order to adjust the on-chip load capacitance value for
frequency compensation of the RTC. Each bit has a different
weight for capacitance adjustment. For example, using a
Citizen CFS-206 crystal with different ATR bit combinations
provides an estimated ppm adjustment range from -34ppm
to +80ppm to the nominal frequency compensation.
X1
C_X1
X2
C_X2
CRYSTAL
OSCILLATOR
FIGURE 12. DIAGRAM OF ATR
The effective on-chip series load capacitance, C_LOAD,
ranges from 4.5pF to 20.25pF with a mid-scale value of
12.5pF (default). C_LOAD is changed via two digitally
controlled capacitors, C_X1 and C_X2, connected from the X1
and X2 pins to ground (see Figure 12). The value of C_X1 and
C_X2 is given by Equation 1:
CX = (16 ⋅ b5 + 8 ⋅ b4 + 4 ⋅ b3 + 2 ⋅ b2 + 1 ⋅ b1 + 0.5 ⋅ b0 + 9)pF
(EQ. 1)
The effective series load capacitance is the combination of
C_X1 and C_X2:
CLOAD
=
----------------¹------------------
⎛
⎝
-----¹-----
C_X1
+
C^-----1_X^----₂^{-⎠⎞}
(EQ. 2)
CLOAD
=
⎛
⎝
-¹--⁶-----^â‹---^b---⁵----⁺-----⁸----^â‹---^b---⁴-----⁺----⁴----^â‹---^b----³----⁺----²-₂----^â‹---^b---²----⁺----¹-----^â‹---^b---¹----⁺-----⁰---^.-⁵----^â‹----^b---⁰----⁺----⁹--_⎠⎞
p
F
For example:
C_LOAD(ATR = 00000) = 12.5pF,
C_LOAD(ATR = 100000) = 4.5pF, and
C_LOAD(ATR = 011111) = 20.25pF.
The entire range for the series combination of load
capacitance goes from 4.5pF to 20.25pF in 0.25pF steps.
Note that these are typical values.
DTR Register - DTR2, DTR1, DTR0: Digital
Trimming Register
The digital trimming Bits DTR2, DTR1 and DTR0 adjust the
number of counts per second and average the ppm error to
achieve better accuracy.
DTR2 is a sign bit, where:
DTR2 = 0 means frequency compensation is >0.
DTR2 = 1 means frequency compensation is <0.
DTR1 and DTR0 are scale bits. DTR1 gives 10ppm
adjustment and DTR0 gives 20ppm adjustment.
12
FN6371.3
August 13, 2008