Philips Semiconductors

PCA8565

Real time clock/calender

Product data

Rev. 01 — 31 March 2003

10 of 26

9397 750 10695

© Koninklijke Philips Electronics N.V. 2003. All rights reserved.

operating at a frequency of at least twice the selected timer clock.

8.7 EXT_CLK test mode

A test mode is available which allows for on-board testing. In such a mode it is

possible to set up test conditions and control the operation of the RTC.

The test mode is entered by setting bit TEST1 in control/status1 register. Then

pin CLKOUT becomes an input. The test mode replaces the internal 64 Hz signal

with the signal applied to pin CLKOUT. Every 64 positive edges applied to

pin CLKOUT will then generate an increment of one second.

The signal applied to pin CLKOUT should have a minimum pulse width of 300 ns and

a minimum period of 1000 ns. The internal 64 Hz clock, now sourced from CLKOUT,

set into a known state by using bit STOP. When bit STOP is set, the pre-scaler is

reset to 0 (STOP must be cleared before the pre-scaler can operate again).

From a STOP condition, the first 1 second increment will take place after 32 positive

edges on CLKOUT. Thereafter, every 64 positive edges will cause a 1 second

increment.

Remark: Entry into EXT_CLK test mode is not synchronized to the internal 64 Hz

clock. When entering the test mode, no assumption as to the state of the pre-scaler

can be made.

Operation example:

1. Set EXT_CLK test mode (control/status 1, bit TEST1 = 1)

2. Set STOP (control/status 1, bit STOP = 1)

Table 24:

Timer control (address 0EH) bits description

Bit

Symbol

Value

Description

7

TE

0

timer is disabled

1

timer is enabled

1 to 0

TD1 and

TD0

timer source clock frequency select; these bits determine the source clock for the

countdown timer, see Table 25; when not in use, TD1 and TD0 should be set to

1

⁄

Table 25:

TD1 and TD0: Timer frequency selection

TD1

TD0

TIMER Source clock frequency

0

0

4096 Hz

0164 Hz

101 Hz

11

1

Table 26:

Timer (address 0FH) bits description

Bit

Symbol

Value

Description

7 to 0

timer

00 to FF

countdown value = n; CountdownPeriod

n

SourceClockFrequency

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