Real-Time Clock (DS 1215)
OPERATION
To access the real-time clock in an STD DOS system, use the DOS
functions "Time" and "Date" when at the DOS command line, or use
interrupt 1Ah function 2 to get to the real-time clock when running an
application program. STD DOS keeps a software clock for its own
time and date, which saves time in accessing the real-time clock on
board. The actual real-time clock is accessed only during time or date
changes to the clock from the command line or through the BIOS
function 2 call. DOS updates the software clock on intervals set by
Timer 0, its System Tick. See Chapter 11 for further details on the
Timer 0 System Tick. The following detailed description of the
timekeeper pertains to direct access of the real-time clock by non-
STD DOS systems.
Communication with the timekeeper is established by pattern
recognition of a serial bit stream of 64 bits. The processor must first
perform a read at the base address of the associated RAM to reset the
pattern comparison circuit of the timekeeper. This RAM base address
is determined by the settings of jumpers W57-59 (as described in
Appendix A) and is the address at which the timekeeper is always
accessed.
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