A Motorola 68000 microprocessor-based data acquisition system incorporates memory ( EPROMS and SRAMS), an Analog-to-Digital Converter (A/D), a Centronics Parallel Printer, and a very simple I/I Device made up of a single push-button switch. There is a total of 8K Bytes of EPROM and 8K Bytes of SRAM. The A/D is microprocessor-compatible. The push-button switch will be used to cause interrupt to the microprocessor. The A/D and Printer are 8-bit devices.
The switch's interrupt to the microprocessor is via INTERRUPT level 6. Even though the interrupting push-button switch does NOT support VECTORED interrupt, a vectored interrupt scheme will be used where some external circuitry will be used to generate the interrupt vector (NOT autovector). An interrupt vector of 70 (decimal) will be generated during IACK.
The system works as follows. The microprocessor sits in a dummy loop. When push-button switch is struck, it interrupts the microprocessor. The interrupt subroutine accomplishes the following tasks. The microprocessor commands the A/D to convert, polls for end of conversion and reads a byte. A copy of the byte is sent to memory. The microprocessor polls the Printer and prints the byte. The system then goes back to the dummy loop until another keystroke occurs and the interrupt process repeats to process another byte. After 32 push-button strikes and 32 interrupts, the microprocessor no longer accepts interrupt from the push-button.
A. Devise your own memory (address) map for the whole system, sketch that memory map to indicate exactly where each device (memory or I/O) will sit on the map. Provide the beginning and ending addresses of all devices. You are allowed to use partial decoding.
B. Provide the address decoding table for the system.
C. Design the logic for the address decoder, glue logic and DTACK, and interconnections to memory, A/D, Printer and Push-button switch's interrupt generation and interrupt acknowledgment circuitry.
D. Write the 68000 assembly language routine that represents the initialization of the vector table. Specify your own addresses for whatever parameters you need.
E. Write the collection of the 68000 assembly language routines that together from the Interrupt Subroutine for the push-button switch. Please provide meaningful comments for your programs. Modularize you program so that it is very clear which section is accomplishing what task.