User`s guide

3.5 ISA Bus Devices
3.5.2 Keyboard and Mouse Controller
The Intel N8242 located on the ISA utility bus provides the keyboard and
mouse controller functions. It is packaged in a 44-pin plastic leadless chip
carrier (PLCC) configuration.
The 8242 is an Intel UPI™-42AH universal peripheral interface. It is an 8-bit
slave microcontroller with 2KB of ROM and 256 bytes of RAM that has been
preprogrammed with a keyboard BIOS for standard scan codes.
Refer to Intel document UPI™-41AH/42AH Universal Peripheral Interface
8-Bit Slave Microcontroller for additional information.
3.5.3 Time-of-Year Clock
The Dallas Semiconductor DS1287 chip, located on the ISA utility bus,
provides the time-of-year (TOY) function. It is packaged in a plastic 24-pin
DIP configuration. The DS1287 is designed with onchip RAM, a lithium energy
source, a quartz crystal, and write-protection circuitry. (See Figure 3–3.)
The functions available to the user include:
• A nonvolatile time-of-day clock
• An alarm
• A 100-year calendar
• Programmable interrupt ability
• A square-wave generator
• 50 bytes of nonvolatile SRAM
Contents of the time-of-day register 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 s 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 multiplexer.
Functional Description 3–11