WO1996015498A1 - Integration of microcontrollers with glue logic - Google Patents

Abstract

A versatile microcontroller (59) has elements of a conventional microcontroller, including firmware, combined with a programmable logic array (45) on a single integrated circuit. In a preferred embodiment, the logic elements of the programmable logic portion of the microcontroller are programmable to form a circuit for measuring the oscillating frequency of connected signal.

Description

Integration of Microcontrollers With Glue Logic

Field of the Invention

The present invention is in the area of single-chip microprocessor-based microcontrollers in integrated circuit technology, and pertains in particular to integration of microcontrollers with other solid state circuitry, particularly with circuitry used for dealing with high frequency phenomena.

Background of the Invention

Microcontrollers are in common use in electronic systems and products, particularly for control purposes. For products whose features range from simple functionality to the ability to do complex calculations, microcontrollers serve as hardware intelligence. Such systems and products can vary in complexity from such as a dishwasher or automatic toaster to a top-of-the-line personal computer.

Microcontrollers come in many varieties. They vary in cost, capacity, speed and features. This broad variability allows microcontrollers to be effectively implemented in many different and specialized applications. For example, some microcontroller variations may include an Analog to Digital (A/D) Converter to interface with an external analog sensor, or an internal timer for clock-type applications. Not all features are available in every microcontroller.

Although there are broad variations in different kinds of microcontrollers, as described above, all microcontrollers still have at least one common characteristic; they all contain some sort of solid- state non-volatile memory to hold a code routine for operating the microcontroller. A microcontroller's code routine is its operating instruction set, providing for each microcontroller a particular function or the decision-making ability to choose from a set of functions based on some external input to the microcontroller. In general, non-volatile memory for a microcontroller is either programmable by the designer after manufacture, such as by laser techniques, or the instruction set is be provided by a masking technique in the processes of IC manufacture. Such programming provides for microcontrollers to be configured or customized to many different applications. Furthermore, an instruction set in a microcontroller typically comprises distinct commands which execute sequentially, one command after another, in time increments of typically microseconds.

The rate at which a microcontroller can function, that is, run its control program, is a function of a number of variables, such as the specific chip design, which limits, for example, signal propagation rate. So, for all practical purposes, every microcontroller design is limited in operating speed, and consequently, microcontrollers are operated at a speed within their ability to function.

Despite the features available in microcontrollers and the considerable ability to customize and configure available to a system designer via control routines, a microcontroller cannot always provide all of the electronics for a complete electronic system or product. Typically, microcontrollers must interface to circuits outside the microcontroller IC, and quite often a microcontroller may lack necessary characteristics and features needed to complete this interface. For example, the control routines in a microcontroller may not run fast enough to accurately measure or otherwise deal with a rapidly varying external stimulus.

In circumstances where a microcontroller does not comprise the necessary interface circuitry, additional external logic must be used to interface the microcontroller to other circuitry. This external logic can be in the form of discrete standard logic or Programmable Logic Devices (PLDs).

A simple example of the situation described above, where a microcontroller cannot interface directly, is the example of a general frequency measurement system wherein the frequency of oscillation of a signal external to a microcontroller is to be determined. The example system utilizes a very stable time base, such as the microcontroller's crystal oscillator, as a reference. For a predetermined time period both the oscillations of the reference signal and the external signal are counted, and the ratio of the two signal counts is used to derive the frequency of oscillation of the external signal.

In the example given, almost any microcontroller can handle the frequency calculation easily. But not all microcontrollers are capable of measuring both input signals, because some microcontrollers offer on-board counters as an option while others do not. Even in cases where the microcontroller has a counter, the counter start and stop functions may be accessible only through control routines.

Another potential problem is the speed with which the microcontroller executes its internal control routines. If the execution rate isn't fast enough to stop the reference signal counter within the space of a single count, extra reference signal counts may be added, limiting the accuracy of a computed signal ratio. And in many applications, microcontrollers must handle a variety of functions. Since microcontrollers execute control code sequentially, they may not be fast enough or have the time to allow real-time response.

One alternative in the counter example is simply to select a very fast microcontroller, but this is not a very satisfactory solution.

Another, more often used, alternative is to implement counters in hardware external to the microcontroller. In this solution, external counters are specifically hard wired to perform simultaneous external and reference signal counting. Such external counters respond immediately to both signals, and are not limited by execution time. More specifically, the external counters are dedicated to a single function. With such external counters in place, the microcontroller 4 19

- 4 • task is reduced to reading in data from the external hardware whenever it is appropriate, and then doing the frequency calculations.

As illustrated by the example above, microcontrollers offer great advantages in flexibility, and the ability to make decisions and perform calculations, but microcontrollers are also limited in the feature sets that they offer and by the execution time of their control routines. In applications or portions of applications that require real¬ time response, or have well-defined singular functions, dedicated, hard-wired circuits are often conventionally required.

One way to implement external circuitry to a microcontroller is with discrete standard logic. This is typically the simplest way, as no special equipment is needed to design and implement a circuit using discrete standard logic components. This solution, however, has several disadvantages. For one thing, the parts count is high, discrete standard logic occupies board real estate, and once designed and implemented, such a system is inflexible. Discrete standard logic implementations are not easily modified for future design enhancements or changes. Very often, changes require additional parts or significant changes to printed circuit board (PCB) layouts, adding to overall system cost.

A more flexible way to achieve external hardware needed is through a PLD. Such devices, often called Gate Array Logic (GAL) or Programmable Array Logic (PAL), contain programmable hardware logic circuitry that can reproduce almost any function that can be implemented in discrete standard logic. Programmable Array Logic devices are described briefly in Microprocessor Based Design by Michael Slater, © 1989 by Prentice-Hall, Inc. at page 182, fourth paragraph, incorporated herein by reference. PALs are also the subject of the Programmable Array Logic Handbook, available from Monolithic Memories, Santa Clara, CA. Another helpful reference is Integrated Circuit Design and Technology. © 1990 by Martin J. Morant; pages 97-107. This reference also discusses Gate Array Logic. All of these are incorporated herein by reference.

PLDs are also often called glue logic for the way they can be attached (glued) to systems to further customize such circuits. After being programmed, a PLD functions as a hard-wired discrete standard logic circuit that is contained in one package, and once programmed and implemented in the system, future upgrades or changes to a system can be done by just re-programming the existing PLD or programming a similar PLD and putting the new PLD in place of the old one.

With the use of PLDs, part count is lowered, because a single PLD has the ability to duplicate the functionality of a large number of discrete standard logic parts. Overall PCB space used is less, and PCB re-layout can be significantly reduced, depending on the complexity of the needed function. In general, too, overall cost will be less than for a discrete standard logic implementation.

Thus, by taking advantage of semiconductor integration, PLDs can provide a system that is cheaper, more flexible and smaller in size than can be done with discrete standard logic.

But even an external PLD solution has limitations relative to small and portable electronic systems and products. In today's marketplace, designers of portable and hand-held electronic products face the challenge of squeezing additional functionality into products of ever smaller size, and a PLD package can take up needed and costly PCB space.

In current technology, microcontrollers and PLDs are not combined. What is clearly needed is an integrated circuit (IC) that combines the functions of a microcontroller and PLD in one package.

Summary of the Invention

In a preferred embodiment of the present invention an integrated circuit comprises a microcontroller portion configured for performing a specific algorithm and providing a result; and a programmable logic portion connected to the microcontroller portion. The programmable logic portion is alterable to provide two or more different logic functions. In various embodiments, programmability may be by laser operations or electrical operations, in the manner of commercially available programmable logic arrays.

Combination of glue logic functions with microcontroller functions in one IC results in a reduction of chip count and space requirements on a PCB, thus permitting greater functionality in small products. Additionally, having a single IC instead of two or more provides cost savings in manufacturing, and since only one package is needed to house the IC, a single IC will also lead to cost savings in IC packaging. Furthermore, interconnect density on a PCB will also be greatly reduced resulting in higher reliability, as PCB's will be less prone to fail due to interconnect failure. Thus, combining a microcontroller and PLD in one IC will create a single packaged product that is highly customizable in both software and hardware, further simplifying system integration and future system upgrades and changes.

In embodiments of the present invention, combining the functions of a microcontroller and a PLD in one IC package will result in system chip count reduction and PCB space savings, thereby creating a single packaged product that is less expensive to manufacture, more in system reliable and highly customizable in both hardware and software.

Brief Description of the Drawings

Fig. 1 is a block diagram of a general frequency measurement system implemented with a microcontroller and external standard digital logic.

Fig. 2 is a block diagram of a general frequency measurement system implemented with a microcontroller and an external PLD.

Fig. 3 is a block diagram of a general frequency measurement system implemented with an integrated microcontroller and PLD IC according to an embodiment of the present invention.

Description of the Preferred Embodiments

In the descriptions of the prior art and the present invention below, the same example described in the Background section is used.

Fig. 1 is a block diagram of a general and conventional external frequency measurement system 11 along with a frequency source 13 and signal conditioning circuit 15. Frequency source 13 provides an oscillating signal on line 17 whose frequency of oscillation is to be determined by frequency measurement system 11.

Before being input into frequency measurement system 11, the signal on line 17 must be conditioned by signal conditioning circuit 15. This is necessary in order to turn the signal on line 17 into a format that is readable by and not destructive to frequency measurement system 11. The signal conditioning is typically a requirement in such systems, but has no particular bearing on the invention.

The output of signal conditioning circuit 15 is input into frequency measurement system 11 where oscillations are counted by external counter 19.

Along with external counter 19, frequency measurement system 11 comprises a reference counter 21 and a microcontroller 23. In this implementation, both external counter 19 and reference counter 21 are implemented with discrete standard logic elements.

In frequency measurement system 11, based on counts from external counter 19 and reference counter 21, microcontroller 23 performs calculations needed to derive the frequency of oscillation of the signal on line 17. Microcontroller 23 reads in data from external counter 19 through data line 33 and from reference counter 21 through data line 29. Also, microcontroller 23 controls the enabling and disabling of external counter 19 and reference counter 21 through control line 31.

Crystal oscillator 25 provides an accurate frequency standard for internal hardware synchronization and control routine execution in microcontroller 23. Additionally, the frequency signal produced by crystal oscillator 25 is provided to reference counter 21 on line 27 to provide an accurate timing reference for measuring the frequency of oscillation of the signal on line 17.

External counter 19 and reference counter 21 are synchronized to each other, separate from microcontroller 23. After external counter 19 and reference counter 21 are enabled by microcontroller 23 through control line 31 to begin counting, a rising signal edge from the output of the signal conditioning circuit starts counter 19 and triggers counter 19 to send a start signal to reference counter 21 through start/stop line 35. Thus, external counter 19 and reference counter 21 are very tightly coupled with both counters beginning their counts substantially simultaneously.

Once external counter 19 reaches a preset number of counts, counter 19 sends a stop signal through start/stop line 35 to stop reference counter 21. In this example, the preset number of counts is hardware coded into external counter 19. External counter 19 stops counting and the stop signal is sent almost immediately after this preset number of counts is reached.

With external counter 19 and reference counter 21 both stopped, microcontroller 23 can read their data counts through data lines 29 and 33 and perform the calculations needed to derive the frequency of oscillation of signal 17. The calculation is quite simple, being the ratio of the reference counts to the counts of counter 19 times the reference frequency.

Since both counters have stopped counting, the execution of control code on microprocessor 23 will not impact the accuracy of the frequency calculation of signal 17.

Fig. 2 is a block diagram of a general external frequency measurement system 37 along with a frequency source 39 and a signal conditioning circuit 41. In the example of Fig. 2, PLD 45, which is a single chip that can be programmed to perform a variety of functions, including the counter functions required for this example, provides the function performed by external counter 19 and reference counter 21 in Fig. 1. A PLD device for element 45 may be selected from a variety of commercial offerings.

Microcontroller 47 and crystal oscillator 49 are the same as microcontroller 23 and crystal oscillator 25 in Fig. 1. The frequency of oscillation of the signal on line 43 from frequency source 39 and conditioned by signal conditioning circuit 41 is calculated by microcontroller 47 with the same methodology as in the configuration of Fig. 1. In order to provide an accurate timing reference for measuring the frequency of oscillation of the signal on line 43, the signal from crystal oscillator 49 is provided on line 51 to PLD 45. External counter and reference counter functions are provided by PLD 45, and data from each is provided to the microcontroller on data lines 55 and 53, respectively. Control line 57 enables external and reference counters in PLD 45.

Functionally, nothing is essentially different between the implementation in Fig. 1 and Fig. 2. But with the implementation in Fig. 2, an increase in flexibility and a decrease in PCB area results from the use of PLD 45 instead of the discrete standard logic counters used in Fig. 1. PLD 45, depending on the specific device used, may provide for reprogramming to increase the number of bits in a counter, providing more resolution to the frequency calculation of signal 43.

An added advantage for the implementation of Fig. 2 is that a single part such as PLD 45, instead of two discrete counters such as external counter 19 and reference counter 21 in Fig. 1, provides savings in PCB space and parts costs. Furthermore, PCB interconnect density is reduced. Start/stop line 35 implemented in measurement system 11 of Fig. 1 is not needed in system 37 of Fig. 2. Furthermore, synchronization between external and reference counters in system 37 is implemented internally within PLD 45 requiring no external connection. This can be a tremendous advantage in larger and more complex systems needing a large amount of standard logic functions that are interconnected.

Fig. 3 is a block diagram of a preferred embodiment of the present invention depicting a general external frequency measurement system 59 consisting of a combined microcontroller and PLD in a single IC 67, along with a frequency source 61 and a signal conditioning circuit 63. In this configuration, IC 67 supplies the functionality performed by microcontroller 23, external counter 19 and reference counter 21 in Fig. 1 and microcontroller 47 and PLD 45 in Fig. 2. Crystal oscillator 69 is the same as crystal oscillator 25 in Fig. 1 and crystal oscillator 49 in Fig. 2.

The frequency of oscillation of the signal on line 65 provided by frequency source 61 and conditioned by signal conditioning circuit 63 is calculated by the same method as in the configurations in Fig. 1 and Fig. 2.

It must be emphasized that, in the example of Fig. 3, the glue logic functionality of the PLD portion of the single IC 67 is not limited to providing counters and control for the counters as in the measurement system described. Depending upon the array of programmable logic provided on the single IC, many other functions might be performed, allowing IC 67 to be configured as a microcontroller for a variety of functions.

Also to be emphasized is that the implementation shown is definitely not an ASIC approach, which is dedicated to a single functionality. The key to the invention is that there is a range of glue logic available to a user so a microcontroller according to the invention may be configured in a number of different ways for a number of different purposes.

By combining the functionality of a microcontroller and PLD in one IC, system 59 provides additional advantages to those described for system 37 in Fig. 2. For example, parts count is reduced to a minimum by having one packaged IC instead of at least two, which leads to additional savings in PCB space and parts costs, and since all interconnect is handled internally within IC 67, external connections are eliminated, reducing overall PCB interconnect density. Also, the control and data lines utilized in system 37 in Fig. 2 are implemented within IC 67.

Combined microcontroller and PLD IC 67 is highly amenable to customization in both software and hardware making it easy to interface to a wide variety of applications without any, or with substantially fewer additional parts than conventionally required, depending on design complexity. Overall system design is simpler and less dense, resulting in a less expensive system that has considerable flexibility for future system changes or upgrades.

It will be apparent to one with skill in the art that there are many changes that might be made without departing from the spirit and scope of the invention. For example, although a general external frequency measurement system is used to illustrate an embodiment of the invention, combined microcontroller and PLD IC 67 is not limited to just that particular application. Many other simple and complex systems can benefit from a combined microcontroller and PLD IC, such as, for example, a keyboard controller for a personal computer or a position encoder system.

As another example, a microcontroller can be combined with other types of programmable hardware logic in order to produce the same functionality as a combined microcontroller and PLD IC. Programmable hardware logic is not limited to PLDs, such as GALs and PALs, and includes all of the class of ICs generally known as Glue Logic. There are a variety of ways the resulting functionality may be implemented, providing a package less expensive to manufacture, more compact and more flexible than in current art.

Claims

What is claimed is:

1. An integrated circuit comprising: a microcontroller portion configured for performing a specific algorithm and providing a result; and a programmable logic portion connected to the microcontroller portion; wherein the programmable logic portion is alterable to provide two or more different logic functions.

2. An integrated circuit as in claim 1 further comprising a sequence of registers accessible in sequence to the microcontroller, for storing a sequence of commands executable by the microcontroller to process data provided by the programmable logic portion.

3. An integrated circuit as in claim 1 wherein the programmable logic portion is alterable by laser programming techniques.

4. An integrated circuit as in claim 1 wherein the programmable logic portion is alterable by electrical programming techniques.

5. An integrated circuit as in claim 1 wherein the programmable logic portion includes elements arrangable as counters for counting oscillation frequency of incoming signals.

6. A method for providing a specific-purpose microcontroller, comprising the steps of: combining a microcontroller and a programmable logic array on a single IC; and programming the programmable logic array to provide at least one glue logic function connected to the microcontroller on the single chip.

7. The method of claim 6 wherein the at least one glue logic function includes a counter with an external connection from the single IC chip.

8. A system for measuring frequency of an oscillating signal, comprising: a signal-conditioning circuit with an input for receiving the oscillating signal to be conditioned and an output for providing the conditioned signal to other circuitry; and a combined single-chip microcontroller and programmable logic array having the programmable logic array programmed to provide one counter for receiving and counting oscillations of the conditioned signal, and to provide a second counter for receiving and counting oscillations of a reference signal having a known frequency.