PCA5010H datasheet(34/112 Pages) PHILIPS

34 / 112 page

1998 Nov 02

Philips Semiconductors

Product speciﬁcation

Pager baseband controller

PCA5010

Fig.18 Synchronization of local counter operation and access from the microcontroller.

handbook, full pagewidth

MGR119

SET (SFR)

76.8 kHz

SET flag (local)

store (local)

data (SFR)

data (local)

counter

reload from

local data

− 1

− 2

− 3

− 4

− 1

− 2

6.12

6 MHz oscillator

6.12.1

FUNCTION

The 6 MHz oscillator provides the clock for the DC/DC

converter, the I2C-bus interface, the port I/Os and for the

external memory access timing (ALE/PSEN).

The 6 MHz oscillator is a 5 inverter stage current

controlled ring oscillator. The oscillator is optimized for low

operating current consumption.

The actual frequency of the oscillator can be measured by

activating the MFR signal. An 8-bit counter will then be

reset and will start counting at the first rising edge of the

76.8 kHz signal and stop counting at the next rising edge

of the 76.8 kHz signal. The processor then can read the

contents of the MFR counter.

The processor can adjust the oscillator frequency using

the F0 to F4 signals (control of source current for ring

oscillator).

The 6 MHz oscillator is enabled by hardware only during

the start-up phase and whenever the DC/DC converter

needs the 6 MHz clock. In all other cases the 6 MHz

oscillator is switched of by hardware.

The DC/DC converter does not need the 6 MHz clock

when set in standby mode.

If the 6 MHz output is required as a frequency source for

other blocks (e.g. I2C-bus) the software needs to enable it

explicitly by setting ENB = 1. Besides the DC/DC

converter the following functions require the operation of

the 6 MHz oscillator:

• I2C-bus block as basic time reference

• Port output logic. Software commands that write to the

ports need this clock to complete the operation (if a

program ‘hangs’, this could be the problem).

• Code fetching from external memories needs the clock

for the ALE/PSEN timing (e.g. LJMP 5000H needs this

clock for completion).

When the ENB bit has been set by software, the clock will

be available internally after the start-up time of this

oscillator. The start-up time is 2 to 3 periods of the

76.8 kHz reference frequency.

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