BQ4285_14 Datasheet, PDF (9/29 Pages) Texas Instruments – Real-Time Clock (RTC) With NVRAM Control

bq4285
Control/Status Registers
The four control/status registers of the bq4285 are acces-
sible regardless of the status of the update cycle (see Ta-
ble 4).
Register A
Register A Bits
7
6
5
4
3
2
1
0
UIP OS2 OS1 OS0 RS3 RS2 RS1 RS0
Register A programs:
s The frequency of the square-wave and the periodic
event rate.
s Oscillator operation.
Register A provides:
s Status of the update cycle.
RS0–RS3 - Frequency Select
7
6
5
4
3
2
1
0
-
-
-
- RS3 RS2 RS1 RS0
These bits select one of the 13 frequencies for the SQW out-
put and the periodic interrupt rate, as shown in Table 3.
OS0–OS2 - Oscillator Control
7
6
5
4
3
2
1
0
- OS2 OS1 OS0 -
-
-
-
These three bits control the state of the oscillator and di-
vider stages. A pattern of 010 enables RTC operation by
turning on the oscillator and enabling the frequency di-
vider. A pattern of 11X turns the oscillator on, but keeps
the frequency divider disabled. When 010 is written,
the RTC begins its first update after 500ms.
UIP - Update Cycle Status
7
6
5
4
3
2
1
0
UIP -
-
-
-
-
-
-
This read-only bit is set prior to the update cycle. When
UIP equals 1, an RTC update cycle may be in progress.
UIP is cleared at the end of each update cycle. This bit
is also cleared when the update transfer inhibit (UTI)
bit in register B is 1.
Register B
Register B Bits
7
6
5
4
3
2
UTI PIE AIE UIE SQWE DF
Register B enables:
s Update cycle transfer operation
s Square-wave output
s Interrupt events
s Daylight saving adjustment
Register B selects:
s Clock and calendar data formats
All bits of register B are read/write.
1
0
HF DSE
Table 4. Control/Status Registers
Reg.
A
Loc.
(Hex) Read Write ^{7 (MSB)}
6
0A Yes Yes¹ UIP na OS2 na
Bit Name and State on Reset
5
4
3
2
OS1 na OS0 na RS3 na RS2 na
1
RS1 na
0 (LSB)
RS0 na
B 0B Yes Yes UTI na PIE 0 AIE 0 UIE 0 SQWE 0 DF na HF na DSE na
C 0C Yes No INTF 0 PF 0 AF 0 UF 0 - 0 - 0 - 0 - 0
D 0D Yes No VRT na - 0 - 0 - 0 - 0 - 0 - 0 - 0
Notes:
na = not affected.
1. Except bit 7.
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