NXP Semiconductors UM10301 PCF2123 - Manual (Page 6)

NXP Semiconductors
UM10301
User Manual PCF85x3, PCA8565 and PCF2123, PCA2125
UM10301_1 © NXP B.V. 2008. All rights reserved.
User manual Rev. 01 — 23 December 2008 6 of 52
The PCA8565 and PCA2125 oscillators operate over a wider temperature range (up to
125 ºC) and are suitable for use in the harsh environments found within automobiles.
Power consumption remains low — only 700 nA at 2 V. Serial interface is I
2
C or SPI.
All the RTCs have ESD protection that exceeds 2000 V HBM per JESD22-A114, 200 V
MM per JESD22-A115. Charge Device Model values vary from 500 V to 2000 V CDM
per JESD22-C101. Refer to the datasheet of the respective device. Latch-up testing,
performed in accordance with JEDEC Standard JESD78, exceeds 100 mA.
3. Comparison
Table 2 on the next page gives a quick overview of the features, specifications and
differences between the RTCs dealt with in this User Manual. The PCF8573 which
belongs to the PCF85x3 family is no longer in production and has thus not been included
in the table. However, this user manual is useful for this type as well.
Further there are some derived types from the main types listed in the table with small
differences in for example delivery form or the number of integrated oscillator capacitors.
Consult NXP for more details.
3.1 Event counter mode
Two real time clocks, PCF8583 and PCF8593, have an extraordinary feature. It is the
event counter mode which can be selected by setting the appropriate bits in the control
register. In this mode the oscillator is disabled and the oscillator input is switched to a
high impedance state. This mode can be used to count pulses applied to the oscillator
input OSCI. There is no crystal in the circuit and OSCO is left open circuit. The event
counter stores up to 6 digits of data. Events are stored in BCD format. The 6 digits use
three 8 bit registers (hundredth of a second, seconds, and minutes). D5 is the most
significant and D0 the least significant digit. Every digit can contain values ranging from 0
to 9 and thus up to 999 999 events can be stored.
It is also possible to set an event counter alarm. When this function is enabled, the alarm
occurs when the event counter registers match the programmed value. In this event the
alarm flag is set. The inverted value of this flag can be transferred to the interrupt pin by
setting the alarm interrupt enable in the alarm control register. In this mode the timer
increments once for every one, one hundred, ten thousand or 1 million events,
depending on the programmed value of the alarm control register. In all other events, the
timer functions are as in clock mode.
Note that immediately following power-on, all internal registers are undefined and must
be defined by software. It is also possible that upon power-on the device is initially in
event-counter mode in which event the oscillator will not operate until the correct settings
are written into the control registers.
The count value will increment on the falling edge. However, after a new count value has
been programmed at least one rising edge must have occurred before events will be
detected on the falling edge.