AN2555 - Application note

Modified features

12/33

1.5

Real Time Clock

The RTC module can be clocked by two different sources: the main oscillator ( pins XTAL1 and XTAL2) or

the 32 kHz low power oscillator (pins XTAL3 and XTAL4). The selection of the clock source can be made

via an additional bit in the RTCCON register.

1.5.1

Hardware impacts

Check the usage of XTAL3 and XTAL4 (respectively pins 143 and 144).

1.5.2

Software impacts

The address range of the RTC registers has been modified from 00’EC00h - 00’ECFFh on the

ST10F269Zx to 00’ED00h - 00’EDFFh on the ST10F276Z5. This change had no impact if the software

uses the register names defined by the toolchains and if the target CPU selection is changed to

ST10F276Z5.

If the software was directly using the address of the RTC register, it must be modified according to new

mapping.

In the ST10F269Zx, both byte and word accesses were allowed for the RTC module. In the ST10F276Z5,

only word accesses are possible. Check that the code is not doing byte accesses to the RTC module.

In addition, new bits have been added into the RTCCON register (OSC, OFF32). There is no impact if the

code was not writing to the upper part of the RTCCON register, which was reserved.

The handling of the RTCAIR and RTCSIR flags (respectively, bit 2 and bit 0 of the RTCCON register) is

also changed:

●

In the ST10F276Z5, these flags are cleared by writing them to 1

●

In the ST10F269Zx, these flags are cleared by writing them to 0

As these flags must be cleared by software when entering the corresponding interrupt service routine, a

change in the application code is needed.

Example for the RTCSIR flag

Replace ST10F269Zx code:

RTCCON &= 0xFFFE;// Clear RTCSIR flag

by the following code for ST10F276Z5:

RTCCON |= 0x0001;// Write 1 into RTCSIR flag to clear it

ST10F269Zx: RTCCON (F1C4h / E2h)

ESFR

Reset Value: --00h

ST10F276Z5: RTCCON (F1C4h / E2h)

ESFR

Reset Value: 0000h

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

--

--

--

--

RTC

OFF

--

-

RTC

AEN

RTC

AIR

RTC

SEN

RTC

SIR

RW

RW

RW

RW

RW

15 14 13 12 11 10

9

8

7

6

5

4

3

2

1

0

------

OFF32 OSC RTCOFF

-

-

-

RTCAEN RTCAIR RTCSEN RTCSIR

RW

R

RW

RW

RW

RW

RW