|ISL12022M||Real Time Clock with Embedded Crystal, ±5ppm Accuracy|
|ISL12022M Datasheet PDF : 27 Pages |
I2C Serial Interface
The ISL12022M has an I2C serial bus interface that provides
access to the control and status registers and the user
SRAM. The I2C serial interface is compatible with other
industry I2C serial bus protocols using a bi-directional data
signal (SDA) and a clock signal (SCL).
The ISL12022M provides both initial timing correction and
temperature correction due to variation of the crystal oscillator.
Analog and digital trimming control is provided for initial
adjustment, and a temperature compensation function is
provided to automatically correct for temperature drift of the
crystal. Initial values for the initial AT and DT settings (ITR0),
temperature coefficient (ALPHA), crystal capacitance (BETA),
as well as the crystal turn-over temperature (XTO), are preset
internally and recalled to RAM registers on power-up. These
values can be overwritten by the user although this is not
suggested as the resulting temperature compensation
performance will be compromised. The compensation
function can be enabled/disabled at any time and can be used
in battery mode as well.
The battery-backed registers are accessible following a
slave byte of “1101111x” and reads or writes to addresses
[00h:2Fh]. The defined addresses and default values are
described in the Table 1. The battery backed general
purpose SRAM has a different slave address (1010111x), so
it is not possible to read/write that section of memory while
accessing the registers.
The contents of the registers can be modified by performing a
byte or a page write operation directly to any register address.
The registers are divided into 8 sections. They are:
1. Real Time Clock (7 bytes): Address 00h to 06h.
2. Control and Status (9 bytes): Address 07h to 0Fh.
3. Alarm (6 bytes): Address 10h to 15h.
4. Time Stamp for Battery Status (5 bytes): Address 16h to
5. Time Stamp for VDD Status (5 bytes): Address 1Bh to
6. Day Light Saving Time (8 bytes): 20h to 27h.
7. TEMP (2 bytes): 28h to 29h.
8. Crystal Net PPM Correction, NPPM (2 bytes): 2Ah, 2Bh
9. Crystal Turnover Temperature, XT0 (1 byte): 2Ch
10. Crystal ALPHA at high temperature, ALPHA_H (1 byte):
11. Scratch Pad (2 bytes): Address 2Eh and 2Fh
Write capability is allowable into the RTC registers (00h to 06h)
only when the WRTC bit (bit 6 of address 08h) is set to “1”. A
multi-byte read or write operation should be limited to one
section per operation for best RTC time keeping performance.
A register can be read by performing a random read at any
address at any time. This returns the contents of that register
location. Additional registers are read by performing a
sequential read. For the RTC and Alarm registers, the read
instruction latches all clock registers into a buffer, so an
update of the clock does not change the time being read. At
the end of a read, the master supplies a stop condition to
end the operation and free the bus. After a read, the address
remains at the previous address +1 so the user can execute
a current address read and continue reading the next
register. When the previous address is 2Fh, the next
address will wrap around to 00h.
It is not necessary to set the WRTC bit prior to writing into
the control and status, alarm, and user SRAM registers.
TABLE 1. REGISTER MEMORY MAP (YELLOW SHADING INDICATES READ-ONLY BITS)
ADDR. SECTION NAME
0 to 59
0 to 59
0 to 23
1 to 31
1 to 12
0 to 99
0 to 6
July 10, 2009
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