DTK PIM-TB10 Руководство пользователя - Страница 4
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A "Dual-in-Line Package (DIP) switch (SWI) (one eight
switch pack) is mounted on the board and can be read under
program control.
The 0 I P !;wi tch provides the system software·
with information about the installed options, how much storage
the system board has, what type of the display adapter is installed,
what operation modes
ar~
desired when power is switched on
(color or black-and-white, 80- or 40-character lines), and the
nL'mb£r of diskette drive attached.
The system board consists of five functional area: the proces
sor subsystem and its support elements, the Read-Only Memory
(ROM) subsystem, the ReadlWrite (RIW) Memory subsystem,
integrated I/O adapters, and the I/O channel. All are desired in
this section.
The heart of the 10MHZ Turbo system board is. the INTEL
8088-1 or qualified 8088-2 microprocessor. This processor is a"
8-bit external bus version of INTEL'S 16 bit 8086 processor, and
it's softwarecompatible with the 8086. Thus, the 8088 supports 16
bit operations. including multiply and divide, and supports 20
bits addressing (1 megabyte of storage).
It also operates in a maximum mode, so a coprocessor can be
added as a feature.
The processor operates in two mode, which
can be switched, called Normal mode and Turbo mode. When the
processor operating at 4.77 ,111HZ called Normal mode, the tre
=1uency, which is derived from a 14.318 MHZ crystal, is devided
by 3 for the processor clock, and by 4 to obtain the 3.58 MHZ
color burts signal required for color television.
When processor
operating at 10 MHZ called Turbo mode, the frequency is derived
from 30 MHZ.
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-OMA-
Three of the four DMA channels are available on the I/O bus
and support high speed data transfers betwt*3n I/O devices and
memory without processor intervention. The fourth DMA chan
nel is programmed to refresh the system dynamic memory. Th is is
done by programing a channel of the timer-counter device to
periodically request a dummy DMA transfer. This action creates a
. memory-read cycle, which is available to refresh dynamic storage,
both on the system board and in the system expansion slots. All
DMA data transfers. except the refresh channel, take five proces
sor clocks of 210 ns, or 1.05, IJS if the processor ready line is not
deactivated. Refresh DMA cycles take four clocks or 840 ns.
-TIMER
The three programmable timer/counters are used by the
system as follows: Channel
0
is used as a general pl,trpose timer,
providing a constant time base for implementing a time-of-day
clock; ChClnnel 1 is used to time and request refresh cycles from
the DMA channel; and Channel 2 is used to support the tone
generation for the audio speaker.
Each channel has a minimum
timing resolution of 1.05
p.s.
- INTERRUPT
Of the eight prioritized levels of interrupt. six are bussed to
the system expansion slots for use by features cards. Two levels
are used on the system board.
Level 0, the highest priority, is
. attached to Channel 0 of the timer/counter and provides a per
iodic interrupt for the time-of-day clock.
Level 1 is attached
to the keyboard adapter circuits and receives an interrupt for
~ach
scan code sent by the keyboard.
The Non-Maskable Interrupt
(NMi) of the 8088 is used to report memory parity errors.
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