Intel mcs-48 manual InterMODEL225 System Components, Integral CRT, Peripheral Interface, Control

interMODEL225

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'sversatile 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-

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.

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