Zenith Z-100 PC series Service Manual page 84

Page
3-2
Theory of Operation
Busses -- The 8088-2 microprocessor and gate array communicate with
the other devices on the CPU/memory card and with the rest of the
computer system using three busses. Many of the transmissions over these
busses are multiplexed.
The address bus is used to locate the specific device or memory byte that
the microprocessor is seeking. The data bus is used to exchange
information between the microprocessor and the rest of the computer
system. The control bus carries commands to the rest of the system
hardware. This bus carries the read and write signals for the system, the
interrupts from the system, and various other timing and control signals.
The buffers shown on the busses are used to control the direction of the
data flow and buffer the data so that several devices can be driven by
each bus. The multiplexer on the address bus is used to multiplex the
address information for the three banks of RAM on the CPU/memory
card.
8088-2 Microprocessor -- The 8088-2 microprocessor is the heart of the
computer system. It receives inputs from the peripherals and keyboard,
calculates all solutions, and controls the computer system. This
microprocessor is manufactured using HMOS techonology and has 16-bit
internal architecture.
It
uses an 8-bit data bus to communicate with other
devices.
NOTE: This device is capable of operating at clock frequencies of up to
8 MHz and is therefore not interchangeable with an 8088 microprocessor.
Optional 8087-2 Numeric Data Coprocessor -- The 8087-2 coprocessor
may be installed on the CPU/memory card as an option. The 8087-2 is an
ALU processor which contains expanded 80-bit registers, an expanded
instruction set, and internal logic designed to perform complex
mathematical operations with fewer program instructions than would be
required by the 8088-2.
NOTE: This device is capable of operating at clock frequencies of up to 8
MHz and is therefore not interchangeable with an 8087 numeric data
coprocessor.
Programmable Interval Timer -- The programmable interval timer
contains three independent counters which are used by the computer
system to generate specific time delays. These time delays are used to
update the real-time clock, refresh the dynamic RAM, and provide the
frequencies used to generate tones for the speaker.