You mean, after turning on, the µC reads the RTC and then the clock runs software-driven?
The same happens in every? PC. You could be right. There are timer-driven interrupts.
What happens if you read the clock via GPIB (GCLK get clock), which one is asked, hardware or software clock?
Will the RTC be re-read after a Reset? 37 RESE 7.6.1.1 Perform Device Clear
> The real time clock is provided with a 32.768KHz reference clock
> by the crystal Y1 and is adjusted by means of C8 (the 32.768KHz
> should be monitored between TP1 and TP2 (GND)).
> The microprocessor obtains its clock from an internal oscillator
> controlled by the 4MHz crystal Y1 and the capacitors C2 and C3.
Change the values of C2 / C3?
> 11.5.1.3 Interrupt Routines
> There are two sources of interrupt to the I/O uP in the 2720Gs.
> These are :
> i) Real Time Clock Interrupt
> This interrupt is generated by the real time clock and occurs
> every 500uS (approx.). The uP uses this interrupt to multiplex
> the displays and also for timing functions. The front panel
> RESET key is actioned within this routine also.
Ah, IC102/19 (MC146818) generates the IRQ of IC10/5?? (MPU MC6803G)
This means the 32768 Hz Xtal is the source of RT
Please measure this frequency (2048 Hz?)
Datasheet of MC146818 can be found at page 3-697 (741 of 876):
http://www.bitsavers.org/components/motorola/_dataBooks/1983_Motorola_8-Bit_Microprocessor_and_Peripheral_Data.pdfGenerated interrupts can have various sources. See page 3-712 (756 of 876).