User's guide
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23
3.7 Real Time Clock
The VSBC-6872 provides a Real Time Clock device (RTC), which includes a battery backed-up 32 kByte
SRAM. This RTC is a ST Microelectronics device with part number M48T37V.
The 32 kByte non-volatile SRAM provides flexible user data storage. This device supports an 8-bit bus
interface, and has a direct connection to the MPC8270 60x Bus. It is accessible from the VMEbus through
A24 slave access. Please refer to
3.15 VMEbus Interface
for more information.
This RTC also provides Alarm, Battery Test, and Watchdog functions.
The RTC data are mapped in the SRAM memory map.
For detailed register description, please consult the ST Microelectronics literature
"M48T37V datasheet"
Snaphat
®
Battery
The real-time clock device uses a detachable power source battery. This Snaphat
®
battery contains both
the battery and the crystal and is designed to be snapped onto the RTC device.
Figure 5 - RTC Snaphat
®
battery
The replacement battery pack is ST Microelectronics reference M4T28-BR12SH1
The VSBC-6872 is provided with an installed and calibrated Snaphat
®
battery. Therefore, for
maintenance operation, an authorized operator can replace this Snaphat
®
battery by observing the
following procedure.
1. Turn off the power supply
2. Remove carefully the Snaphat
®
battery. A DIP/IC extractor should be used.
3. Plug the new Snaphat
®
battery in respect with the correct orientation
4. Start a new calibration cycle for an accurate system clock precision
The RTC frequency test (FT) output can be measured on testpoint TP16. Refer to
Figure 3
for location.
To avoid draining battery do NOT place SNAPHAT pins into conductive foam.
For detailed specification and register setting, please consult the following literature:
-
"ST Microelectronics M48T37V datasheet"
-
"ST Microelectronics AN934 Timekeeper calibration application note"
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Содержание VSBC-6872 Series
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