3-12
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Functional Description
3
❏
A 28-pin 330mil SO device containing the real-time clock, the
oscillator, power failure detection circuitry, timer logic, 8KB of
static RAM, and gold-plated sockets for a battery
❏
A SNAPHAT
®
battery housing a crystal along with the battery
The SNAPHAT battery package is mounted on top of the M48T59/T559
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 M48T59/T559 is an 8-bit device, 8-, 16-, and 32-bit accesses
from the ISA bus to the M48T59/T559 are supported. Refer to the
MVME2603/2604 Programmer’s Reference Guide and to the
M48T59/T559 data sheet, both listed in
Appendix D, Related
Documentation
, for detailed programming and battery life information.
Programmable Timers
Among the resources available to the local processor are a number of
programmable timers. Timers are incorporated into the PIB controller and
the Z8536 CIO device (diagrammed in
Figure 1-1 on page 1-2
and
Figure
3-1 on page 3-4
). They can be programmed to generate periodic interrupts
to the processor.
Interval Timers
The PCI-ISA Bridge controller has three built-in counters that are
equivalent to those found in an 82C54 programmable interval timer. The
counters are grouped into one timer unit, Timer 1, in the PIB controller.
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 a timer interrupt for a
time-of-day function.
❏
Counter 1 generates a refresh request signal for ISA memory. This
timer is not used in the MVME2603/2604.
