PCD3350AH datasheet(18/36 Pages) PHILIPS

18 / 36 page

1996 Dec 18

Philips Semiconductors

Product speciﬁcation

8-bit microcontroller with DTMF generator,

256 bytes EEPROM and real-time clock

PCD3350A

REAL-TIME CLOCK

The Real Time Clock (RTC) consists of a 32 kHz crystal

oscillator, a 32 kHz to 1 second or 1 minute divider chain,

an 8-bit Frequency Adjustment Register and the Clock

Control Register. The complete RTC section works

independently of the microcontroller status, even in Idle

and Stop mode.

8.1

Oscillator

The internal 32 kHz oscillator needs an external quartz

crystal with a frequency of 32768.00 Hz (a positive

deviation up to +259

× 10−6 is allowed) and an external

feedback resistor between pins RTC1 and RTC2; 4.7 M

Ω

is recommended. It is controlled by the RUN-bit in the

Clock Control Register.

8.2

Divider chain

The divider chain operates with the 32 kHz oscillator

output and divides this signal down to two clocks with a

period of 1 second or 1 minute. Depending on bit ITS in the

Clock Control Register, the falling edge of the seconds or

minutes clock is used to set the Clock Interrupt Flag (CIF)

in the Clock Control Register.

Since the clock interrupt is used to let the microcontroller

leave the Stop mode, it is ORed to the external interrupt

(CE/T0) and has the same functionality, e.g. it must be

enabled in the Clock Control Register (bit ECI) and by

execution of the instruction ‘EN I’. The clock interrupt will

then be treated as an external interrupt.

Additionally, the divider chain generates a 16 kHz clock

(RCO) that can be routed through derivative port line

DP0.0/RCO, controlled by bit ERCO in the Clock Control

8.3

Frequency adjustment

The frequency adjustment is used to extend the interrupt

time by defining the number of 16 kHz clocks in the

Frequency Adjustment Register that will be counted twice

within the first second period after a minute interrupt.

If the second interrupt is used (ITS = 1), every 60th interval

may be up to 15.3 ms longer than the others as a result of

the frequency adjustment. The adjusted Minute Interrupt

Time (MIT) now shows a maximum deviation of 0.5

× 10−6.

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