Hardware manual

3 Programmers Reference EUROCOM-17-5xx
76 Hardware Manual
3.13 Battery-Backed Parameter RAM and Real-Time Clock
The real-time clock is designed with the MK48T12 or MK48T18
timekeeper RAM from SGS Thomson or DS1644 from Dallas. The chip
combines a 2KBx8 (8KBx8, 32KBx8) CMOS SRAM (parameter RAM) a
bytewide accessible real-time clock, a crystal, and a long life lithium
battery, all in one package. The MK48Txx devices have a battery lifetime
of approximetly 3.7years when the clock oscillator is running. To extend
battery lifetime, the clock oscillator can be stopped. Alternatively a Dallas
DS1642/1643 device can be used, which offers a lifetime of 10years even
if the oscillator is running. The Dallas devices do not offer the feature to
check the internal battery via a battery OK flag like the SGS Thomson
devices do.
3.13.1 Parameter
RAM
The address area of this SRAM is divided into two main partitions:
• system dependent parameter data structure, defined by ELTEC to store
setup parameters for hardware initialization and boot informations for
operating systems,
• eight bytes of the SRAM for the registers of the real-time clock.
The front panel hex switch position '00' uses the configuration values
stored in the basic EPROM rather than values defined in the SRAM. For
more details, see also the RMon description.
Table44: Address Assignment of SRAM/RTC
Address Description
$FEC2.0000 - $FEC2.07F7 Reserved for system configuration values.
The structure of the system configuration values is
defined in the RMon manual.
$FEC2.07F8 - $FEC2.7FF7 Free for user if DS1644 is installed.
$FEC2.7FF8 - $FEC2.7FFF Real-time clock registers. See Section3.13.2 ‘Real-Time
Clock’ for more information.