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66 SBC329 3U VPX Single Board Computer
Publication No. SBC329-HRM/1
5.16 Real Time Clock
The PCH provides an RTC, powered from the P3V3_AUX or the VBAT supply.
When either of these supplies is present, the system clock is maintained; if all power
is removed, the RTC is reset. The RTC module comprises a clock with 1 second
resolution, two banks of static RAM and the following interrupt features:
Time of day alarm, with once-a-second to once-a-month range
Periodic rate 122 μ
s to 500 ms
End of update
The RTC function uses the first 14 bytes of the lower static RAM block, with the first
10 bytes being used for time and date information and the last 4 bytes being used to
configure and report the RTC function. The leap year determination for adding a 29
th
day to February does not take into account the end-of-the-century exceptions.
5.17 I
2
C Bus
The PCH has a single I
2
C bus, supporting SMBus 2.0.
I
2
C devices on the board are connected to this bus as shown below:
Figure 5-6 I
2
C Bus Structure
The table below summarizes the I
2
C slave addresses of the devices in the system.
Where I
2
C addresses are quoted, the 8-bit address is the value that would be used to
write to the device on the bus (i.e. the 7-bit
device address and the LSB set to ‘0’).
Table 5-16 I
2
C Bus Addresses
Device
7-bit Address 8-bit Write Address
PCH (Master)
Master only
Master only
DS1682 ETI
0x6B
0xD6
PCA9560 DIP switch
0x4C
0x98
SPD EEPROM
0x50
0xA0
SPD temperature sensor
0x18
0x30
SPD control registers
0x30 to 0x37 0x60 to 0x6E
PEX 8725 PCIe switch
0x70
0xE0
LIS331HH accelerometer
0x19
0x32