REMOTE
TERMINAL
CPU-PIO/DCH
CONTROLLER
USER
CONSOLE
MODEM
SIGNALS
MODEM
SWITCHING
PAL
IAC
SYSTEM
CONSOLE
FS- 12783
Figure 3-14. DRP Configuration for User Conversation Mode, Block Diagram
3.3.6 Time-of-day Clock/Calendar
The Time-of-Day (TOD) clock/calendar provides a time reference for the ECLIPSE MV/7800 computer during
power-up and hardware reset operations. The TOD values are independent of the real-time clock and
programmed interval timer in the PIO/DCH controller. The TOD clock is connected to the ECLIPSE MV/7800
S-bus through a set of transceivers. It consists of a clock/calendar chip, a 40kHz oscillator module, a 32.768kHz
crystal, a back-up capacitor, a time-slice-timer, an alarm and assorted support logic. The time-slice-timer and
alarm cannot be used simultaneously with the programmed interval timer (PIT) in the PIO/DCH controller
because they both use the PIT register.
The clock/calendar chip is accurate to within 100 microseconds during normal runtime, and drops to one-second
accuracy during hardware reset and power-down periods. During these periods, the time of day is kept by the
clock/calendar chip, which is backed up by a capacitor. The back-up period is at least 24 hours, and typically
lasts 48-64 hours. At power-up time and after a hardware reset, the time of day, to one-second accuracy, is read
from the clock/calendar chip. Microcode waits for the next one-second trick of the clock to minimize the change
of getting duplicate TOD values. Once the clock/calendar chip is read at power-up (or after reset) it is not
referenced again during ECLIPSE MV/7800 operation.
043-003621
3-36
DGC
CONFIDENTIAL - INTERNAL USE ONLY
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