pcf2123 NXP Semiconductors, pcf2123 Datasheet - Page 36

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

NXP Semiconductors
PCF2123_1
Product data sheet
Fig 25. Serial bus read example
address
counter
SDO
SCL
SDI
CE
9.14.1 Interface watchdog timer
R/W
b7
xx
1
b6
0
b5
0
During read/write operations, the time counting circuits are frozen. To prevent a situation
where the accessing device becomes locked and does not clear the interface by setting
pin CE LOW, the PCF2123 has a built in watchdog timer. Should the interface be active for
more than 1 s from the time a valid subaddress is transmitted, then the PCF2123 will
automatically clear the interface and allow the time counting circuits to continue counting.
CE must return LOW once more before a new data transfer can be executed.
Fig 26. Interface watchdog timer
b4
1
a. Correct data transfer: read or write
b. Incorrect data transfer; read or write
b3
0
addr 07
b2
1
WD timer
WD timer
counters
counters
b1
HEX
1
data
data
time
time
CE
CE
b0
1
Rev. 01 — 19 November 2008
b7
0
07
b6
valid sub-address
valid sub-address
0
months data 11
running
running
b5
0
b4
1
b3
0
BCD
b2
data
data
0
time counters frozen
WD timer running
b1
t
0
W(CE)
data
data
time counters frozen
b0
1 s < t
WD timer running
1
< 1 s
b7
data
data
0
W(CE)
08
b6
0
data transfer fail
< 2 s
b5
years data 06
0
SPI Real time clock/calendar
b4
0
running
b3
0
BCD
b2
1
WD trips
PCF2123
© NXP B.V. 2008. All rights reserved.
running
001aai563
001aai564
b1
1
001aaf916
b0
0
09
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