AN968
APPLICATION NOTE
VMEbus TIMEKEEPER Requirements
Surface-mount TIMEKEEPER devices, from STMicroelectronics, are designed explicitly for inclusion on
CPU boards. A typical arrangement is shown in Figure 1.
Figure 1. CP U mo dule with a TIME K E E PE R D e vi ce
Local Microprocessor
Bus Interface
Shared Memory
PCI Bus
Bridge
ISA Bus
TIMEKEEPER
VMEbus
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AN968 - APPLICATION NOTE
Each member of the TIMEKEEPER family provid e s su ppo r t for the follo w ing function s:
■ General timekeeping (i.e. seconds, hour, date, year,...)
■ Time stamping (data collection correlated against time)
■ Event sequencing during the manufacturing proces s
■ Watchdog (to monitor for processes in the system that are out of control)
■ RST: reset signal available for the CPU
■ Non-volatile RAM (to store start-up parameters, ethernet address, etc.)
Most of the members of the TIMEKEEPER family (M48T02, M48T18, M48T559, M48T5X and M48T3X)
are already being used by manufacturers of VME (Versa Module Eurocard) boards. However, the ones
that are best suited for new ‘design-in’ boards are the M48T59, M48T58 and the M48T559. These have
the following features:
■ Automatic chip deselect and write protect when the power fails (as described in Application Note
AN1012
■ BCD coded year, month, day, date, hours, minutes, and seconds (as described in Application Note
AN923
■ Software calibration for increased clock accuracy (as described in Application Note
■ 8K x 8 non-volatile static RAM (as described in Application Note
■ Microprocessor power-on reset (devices with 16-Byte register maps, only) (as described in Application
Note
■ Battery low warning software bit (devices with 16-Byte register maps, only)
■ WDF interrupt function (devices with 16-Byte register maps, only) (as described in Application Note
AN924
■ Periodic alarms (devices with 16-Byte register maps, only)
■ Industry’s first fully surface mountable TIMEKEEPER solution (as described in Application Note
AN1019
■ Industry’s smallest non-volatile TIMEKEEPER footprint (as shown in Application Note
■ Address/Address/Data Multiplex (M48T559 only) prevents the need for additional latch circuitry (as
described in Application Note
However, the significant feature is that each is available in ST’s revolutionary SNAPHAT package: a
standard SOIC that is surface mounted in the conventional way, and then is fitted with a SNAPHAT top,
as shown in Figure 2, containing the battery and crystal.
)
)
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)
)
AN1012
AN934
)
)
)
AN96 7
AN1019
).
)
Figure 2. SOIC and SNAPHAT Package
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AN968 - APPLICATION NOTE
If you have any questions or suggestions concerning the matters raised in this document, please send
them to the following electronic mail addresses:
apps.nvram@st.com
ask.memory@st.com
Please remember to include your name, company, location, telephone num ber and fax number.
(for application support)
(for general enquiries)
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted
by implic ation or otherwise under any patent or p atent right s of STMicroelectr oni cs. Spec i fications mentioned i n this publicatio n are subject
to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not
authorized for use as cri tical comp onents in life support dev i ces or systems wi thout express written approval of STMicroel ectronics.
© 1998 STMicroelectronics - All Rights Reserved
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