DS1553P Maxim Integrated Products, DS1553P Datasheet - Page 6

• Manufacturer Part Number: DS1553P
• Description: 64K NV Y2KC Real Time Clocks RAM
• Manufacturer: Maxim Integrated Products

SETTING THE CLOCK
The 8th bit, B7 of the Control Register is the write bit. Setting the write bit to a 1, like the read bit, halts
updates to the DS1553 (1FF8h-1FFFh) registers. After setting the write bit to a 1, RTC Registers can be
loaded with the desired RTC count (day, date, and time) in 24-hour BCD format. Setting the write bit to a
0 then transfers the values written to the internal RTC Registers and allows normal operation to resume.
CLOCK ACCURACY (DIP MODULE)
The DS1553 is guaranteed to keep time accuracy to within 1 minute per month at 25 C. The RTC is
calibrated at the factory by Dallas Semiconductor using nonvolatile tuning elements and does not require
additional calibration. For this reason, methods of field clock calibration are not available and not
necessary. Clock accuracy is also effected by the electrical environment and caution should be taken to
place the RTC in the lowest level EMI section of the PCB layout. For additional information see
application note 58.
CLOCK ACCURACY (POWERCAP MODULE)
The DS1553 and DS9034PCX are each individually tested for accuracy. Once mounted together, the
module is will typically keep time accuracy to within 1.53 minutes per month (35 ppm) at 25°C. Clock
accuracy is effected by the electrical environment and caution should be taken to place the RTC in the
lowest level EMI section of the PCB layout. For additional information please see application note 58.
FREQUENCY TEST MODE
The DS1553 frequency test mode uses the open drain
the Watchdog Steering bit (WDS) is a 1 or the Watchdog Register is reset (Register 1FF7h = 00h). The
32.768 kHz RTC oscillator. The
proper operation. The FT bit is cleared to a 0 on power-up.
USING THE CLOCK ALARM
The alarm settings and control for the DS1553 reside within Registers 1FF2h-1FF5h. Register 1FF6h
contains two alarm enable bits: Alarm Enable (AE) and Alarm in Backup Enable (ABE). The AE and
ABE bits must be set as described below for the
condition.
The alarm can be programmed to activate on a specific day of the month or repeat every day, hour,
minute, or second. It can also be programmed to go off while the DS1553 is in the battery backed state of
operation to serve as a system wake-up. Alarm mask bits AM1-AM4 control the alarm mode. Table 3
shows the possible settings. Configurations not listed in the table default to the once per second mode to
notify the user of an incorrect alarm setting.
ALARM MASK BITS Table 3
IRQ
IRQ
AM4
/FT output will toggle at 512 Hz when the FT bit is a 1, the Alarm Flag Enable bit (AE) is a 0, and
/FT output and the frequency test mode can be used as a measure of the actual frequency of the
1
1
1
1
0
AM3
1
1
1
0
0
AM2
1
1
0
0
0
IRQ
AM1
/FT pin is an open drain output which requires a pullup resistor for
1
0
0
0
0
ALARM RATE
Once per second
When seconds match
When minutes and seconds match
When hours, minutes, and seconds match
When date, hours, minutes, and seconds match
IRQ
6 of 19
/FT output to be activated for a matched alarm
IRQ
/FT output. With the oscillator running, the
DS1553