pcf2123 NXP Semiconductors, pcf2123 Datasheet - Page 20

• Manufacturer Part Number: pcf2123
• Description: Spi Real Time Clock/calendar
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCF2123_1
Product data sheet
9.8 Timer functions
To prevent the timer flags being overwritten while clearing AF, a logical AND is performed
during a write access. Writing a logic 1 will cause the flag to maintain its value, whereas
writing a logic 0 will cause the flag to be reset.
Table 22.
The following tables show what instruction must be sent to clear bit AF. In this example, bit
MSF and bit TF are unaffected.
Table 23.
The countdown timer has four selectable source clocks allowing for countdown periods in
the range from 244 s to 4 h 15 min. There are also two pre-defined timers which can be
used to generate an interrupt once per second or once per minute. For periods greater
than 4 hours, the alarm function can be used.
Registers 01h, 0Eh and 0Fh are used to control the timer function and output.
Table 24.
[1]
Table 25.
Register
Control_2
Register
Control_2
Bit
7
6 to 4 COFx
3
2
1 to 0 CTD
Bit
7 to 0 COUNTDOWN_
Values of COF[2:0] see
Symbol
-
TE
-
Symbol
TIMER
Flag location in register Control_2
Example to clear only AF (bit 3) in register Control_2
Register Timer_clkout (address 0Eh) bits description
Register Countdown_timer (address 0Ah) bits description
Bit
7
-
Bit
7
-
Rev. 01 — 19 November 2008
Table
6
-
6
-
Value
-
[1]
0
1
-
00
01
10
11
Value
0h to FFh
35.
5
MSF
5
1
Description
unused
CLKOUT control
countdown timer is disabled
countdown timer is enabled
unused
4.096 kHz countdown timer source clock
64 Hz countdown timer source clock
1 Hz countdown timer source clock
1
Description
countdown value = n;
CountdownPeriod
60
Hz countdown timer source clock
4
-
4
-
3
AF
3
0
=
-------------------------------------------------------------- -
SourceClockFrequency
SPI Real time clock/calendar
2
TF
2
1
n
PCF2123
© NXP B.V. 2008. All rights reserved.
1
-
1
-
Reference
-
Section 9.10
Section 9.8.2
Reference
Section 9.8.2
0
-
0
-
20 of 54