User`s guide

3.9.3 Time-of-Year Clock

The Dallas DS1287 chip, located on the ISA utility bus, provides the time-of-

year (TOY) function. It is contained in a plastic 24-pin dual inline package

(DIP). The DS1287 is designed with onchip RAM, a lithium energy source, a

quartz crystal, and write-protection circuitry (see Figure 3–13).

The functions available to the user include the following:

• Nonvolatile time-of-day clock

• Alarm

• 100-year calendar

• Programmable interrupt

• Square-wave generator

• 50 bytes of nonvolatile static RAM

The time of day and memory are maintained in the absence of power through

the lithium energy source.

The DS1287 includes three separate, fully automatic interrupt sources for a

processor. The alarm interrupt can be programmed to occur at rates from one

per second to one per day. The periodic interrupt can be selected for rates

from 122 µs to 500 ms. The update-ended interrupt can be used to indicate to

the program that an update cycle has completed. The device interrupt line is

presented to the system interrupt PLD.

3.9.4 Utility Bus Memory Devices

The AlphaPC64 utility bus drives the Intel 28F008SA ﬂash ROM. This 1MB,

versatile ﬂash ROM provides nonvolatile memory for operating system and

ﬁrmware support. The ﬂash ROM is split into two 512KB segments. Selection

between the two segments is determined by the value of ﬂash_adr19. This

signal is latched and driven by the interrupt PALs that reside on the ISA bus.

Writinga0toISAlocation 800

selects the lower 512KB; writing a 1 selects

the upper 512KB.

In order for the ﬂash ROM to be written, 12 V dc must be present on the V

pin of the ﬂash ROM. Jumper J16 controls the voltage to this pin. With the

jumper across pins 2 and 3, the contents of the ﬂash ROM can be modiﬁed.

With the jumper across pins 1 and 2, it is protected from write operations

(see Table 2–2).

Functional Description 3–37