PCF8583
NXP Semiconductors
Clock and calendar with 240 x 8-bit RAM
7.4 Counter registers
The format for 24 hour or 12 hour clock modes can be selected by setting the most
significant bit of the hours counter register. The format of the hours counter is shown in
Figure 6.
MSB
7
LSB
0
memory location 04h (hours counter)
reset state: 0000 0000
6
5
4
3
2
1
hours in BCD format:
unit place
ten's place (0 to 2 binary)
AM/PM flag:
logic 0: AM
logic 1: PM
format:
logic 0: 24 hour format, AM/PM flag remains unchanged
logic 1: 12 h format, AM/PM flag will be updated
013aaa371
Fig 6. Format of the hours counter
The year and date are stored in memory location 05h (see Figure 7). The weekdays and
months are in memory location 06h (see Figure 8).
MSB
7
LSB
0
memory location 05h (year/date)
reset state: 0000 0001
6
5
4
3
2
1
days in BCD format:
unit place
ten's place (0 to 3 binary)
year (0 to 3 binary, read as logic 0
if the mask flag is set)
013aaa372
Fig 7. Format of the year and date counter
MSB
7
LSB
memory location 06h (weekdays/months)
reset state: 0000 0001
6
5
4
3
2
1
0
months in BCD format:
unit place
ten's place
weekdays (0 to 6 binary, read as logic 0
if the mask flag is set)
013aaa373
Fig 8. Format of the weekdays and month counter
When reading these memory locations the year and weekdays are masked out when the
mask flag of the control and status register is set. This allows the user to read the date
and month count directly. In the event-counter mode, events are stored in BCD format. D5
is the most significant and D0 the least significant digit. The divider is by-passed.
PCF8583
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© NXP B.V. 2010. All rights reserved.
Product data sheet
Rev. 06 — 6 October 2010
7 of 37
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