A fully 16-bit external data bus 68000-microprocessor is used in the following motor control and instrumentation system. It operates as follows:
1. An operator prepares an 8-bit binary value with a dip switch.
2. A momentary contact switch (single-pole-single throw) connected to only one end of a cross-coupled NAND latch is activated. This sets the output of the latch to a logic one.
3. All this time, the 68000 has been polling the output of the latch.
4. When microprocessor detects a logic one at the output of the latch, it resets the latch to a logic zero by sending a low going pulse to the other input leg of the latch.
5. The microprocessor then reads the 8-bit data from the dip switch and puts the value in memory starting at location called ‘BUFFER' . This same data is sent to a digital-to-analog converter ( D/A) whose output drives a dc motor.
6. The output of the dc motor is connected to a tachometer , whose output is, in turn, connected to an 8-bit microprocessor compatible analog-to-digital converter (A/D). The A/D is connected in a free running configuration.
7. The 68000 reads the A/D output, compares it with the original data from the dip switch, sends the hexadecimal number ‘$42' to an 8-bit LED pack if the compared values are different, and sends the hex. value ‘$99' to the same 8-bit LED pack if the compared values are equal.
8. Finally, a centronics parallel printer port is polled for a low-true printer ready logic signal, and the A/D data is sent to the printer.
A. Provide a hardware design for the system. Partial and simplified decoding is acceptable. Use only the following four addresses for your ports design: $3001 ; $30F1; $30E1; $31F1. Do NOT include interface to memory modules and reset circuits. Design the address decoders, I/O ports (where needed), DTACK circuitry, complete circuit details of dip switch and other switch interconnections, complete circuit details of LED interconnections, input/output ports with appropriate handshaking signals. Clearly label A/D, Printer, D/A signals showing how they connect to other circuits.
B. Provide a well-commented 68000 assembly language program to accomplish the tasks indicated in items 1 thru. 8. Clearly identify the specific polling routines and input/output control software for each input/output device.