inter
MODEL225
System Components
The heart of the
IPC
is
an
Intel NMOS 8-bit micro-
processor, the
8085A-2,
running at
4.0
MHz.
64K
bytes of
RAM
memory are provided on the board
using 16K RAMs.
4K
of
ROM
is provided, pre-
programmed with system bootstrap
"self-test"
diagnostics and the Intellec Series
11/85
System
Monitor. The eight-level vectored priority inter-
rupt system allows interrupts to be
individually
masked. Using
Intel's
versatile
8259A
interrupt
controller, the interrupt system may be user pro-
grammed to respond to individual needs.
Input/Output
IPC Serial Channels - The
I/O
subsystem
in
the
Model
225
consists of two parts: the
10C
card
and
two serial channels
on
the IPC itself. Each serial
channel is
RS232
compatible and is capable of run-
ning asynchronously from
110
to
9600
baud or syn-
chronously from
150
to
56K
baud. Both may
be
connected to a user defined data set
or
terminal.
One
channel contains
current
loop adapters. Both
channels are implemented using
Intel's
8251
A
USART. They can be programmed to perform a
variety of
I/O
functions. Baud rate selection is
accomplished through
an
Intel
8253
interval timer.
The
8253
also serves as a real-time clock for the
entire system.
I/O
activity through both serial
channels is signaled to the system through a
second
8259A
interrupt
controller, operating in a
polled mode nested to the primary
8259A.
IOC
Interface
- The remainder of system
I/O
activity takes place in the 10C. The
10C
provides
interface for the CRT, keyboard, and standard
Intellec peripherals including printer, high speed
paper tape
reader/punch,
and universal
PROM
programmer. The
10C
contains its own independ-
ent microprocessor,
an
8080A-2.
The
CPU
controls
all
I/O
operations as well
as
supervising
communications with the
IPC,
8K
bytes of
ROM
contain all
I/O
control firmware.
8K
bytes of
RAM
are used for
CRT
screen refresh storage. These
do not occupy space in
Intellec Series
II
main
memory since the
10C
is a totally independent
microcomputer subsystem.
Integral CRT
Display - The
CRT
is a 12-inch raster scan type
monitor with a
50/60
Hz
vertical scan rate and
15.5kHz horizontal scan rate. Controls are pro-
vided for brightness and contrast adjustments.
The interface to the CRT is provided through
an
Intel
8275
single-chip programmable
CRT
con-
10-3
troller. The master processor on the IPC transfers
a character
for
display to the
10C,
where it is
stored in RAM. The
CRT
controller reads a line at a
time into its line
buffer
through
an
Intel
8257
DMA
controller and then feeds one character at a time
to the character generator to produce the video
signal. Timing for the
CRT
control is provided by
an
Intel
8253
interval timer. The screen display is
formatted
as
25
rows of
80
characters. The full set
of
ASCII
characters is displayed, including lower
case alphas.
Keyboard - The keyboard interfaces directly to
the
10C
processor via
an
8-bit data bus. The
keyboard contains
an
Intel
UPI_41TM
Universal
Peripheral Interface, which scans the keyboard,
encodes
the characters, and
buffers
the
characters to provide N-key
rollover. The
keyboard itself is a high quality
typewriter
style
keyboard containing the
full ASCII character set.
An
upperllower
case switch allows the system to
be
used
for
document
preparation. Cursor control
keys are also provided.
Peripheral
Interface
A
IJPI-41
Universal Peripheral Interface on the
10C
board provides interface
for
other
standard
Intellec peripherals including a printer, high
speed paper tape reader, high speed paper tape
punch, and universal
PROM
programmer. Com-
munication between the
IPC
and
10C
is maintained
over a separate 8-bit bidirectional data bus. Con-
nectors for the four devices named above, as weli
as
the two serial channels, are mounted directly
on the
10C
itself.
Control
User control is maintained through a front panel,
conSisting of a power switch and indicator,
reset/boot
switch,
run/halt
light, and eight inter-
rupt switches and indicators. The front panel cir-
cuit board is attached directly to the
IPC,
allowing
the eight
interrupt
switches to
connect
to the
primary
8259A,
as
well
as
to the Intellec Series
II
bus.
Integral Floppy Disk Drive
The integral floppy
disk
is controlled by
an
Intel
8271
single chip, programmable floppy
disk
con-
troller. It transfers data via
an
Intel
8257
DMA con-
troller between
an
10C
RAM
buffer
and the
diskette. The
8271
handles reading and writing of
data, formatting diskettes, and reading status,
all
upon appropriate commands from the
10C
microprocessor.
AFN-014248
