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Block Diagram
3
Programmable Timers
Interval Timers
3-14
The SNAPHAT battery package is mounted on top of the MT48T18
device. The battery housing is keyed to prevent reverse insertion.
The clock furnishes seconds, minutes, hours, day, date, month, and
year in BCD 24-hour format. Corrections for 28-, 29- (leap year),
and 30-day months are made automatically. The clock generates no
interrupts. Although the M48T18 is an 8-bit device, 8-, 16-, and 32-
bit accesses from the ISA bus to the M48T18 are supported. Refer
to the MVME1603/MVME1604 Programmer's Reference Guide and to
the M48T18 data sheet for detailed programming and battery life
information.
Among the resources available to the local processor are a number
of programmable timers. Timers are incorporated into the ISA
bridge controller, the Z8536 CIO device (diagrammed in Figure 1-1
and Figure 1-2 for the two base boards), and the VMEchip2. They
can be programmed to generate periodic interrupts to the
processor.
The ISA bridge controller has three built-in counters that are
equivalent to those found in an 82C54 programmable interval
timer. These counters are grouped into one timer unit, Timer 1, in
the IBC. Each counter output has a specific function:
Counter 0 is associated with interrupt request line IRQ0. It
can be used for system timing functions, such as timer
interrupt for a time-of-day.
Counter 1 generates a refresh request signal for ISA memory.
This timer is not used in the MVME1603/MVME1604.
Counter 2 provides the tone for the speaker output function
on the ISA bridge controller (the
can be cabled to an external speaker via the remote reset
connector).
signal which
SPEAKER_OUT
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