Microcontroller Integrated Circuit with Read Only Memory
Microcontroller integrated circuit comprises a processor core which exchanges data with at least one data processing and storage device. The integrated circuit comprises a mask-programmed read only memory containing a generic program such as a test program which can be executed by the microcontroller. The genetic program includes a basic function for writing data into the data progressing or storage device or devices. The write function is used to load a downloading program. Because a downloading program is not permanently stored in the read only memory, the microcontroller can be tested independently of the application program, and remains standard with regard to the type of memory component with which it can be used in a system.
To be more precise, the invention concerns a microcontroller integrated circuit. A microcontroller is usually a VLSI (Very Large Scale Integration) integrated circuit containing all or most of the components of a "computer". Its function is not predefined but depends on the program that it executes.
A microcontroller necessarily comprises a processor core including a command sequencer (which is a device distributing various control signals to the instructions of a program), an arithmetic and logic unit (for processing the data) and registers (which are specialized memory units).
The other components of the "computer" can be either internal or external to the microcontroller, however. In other words, the other components are integrated into either the microcontroller or auxiliary circuits.
These other components of the "computer" are data processing and storage devices, for example read only or random access memory containing the program to be executed, clocks and interfaces (serial or parallel).
As a general rule, a system based on a microcontroller therefore comprises a microchip containing the microcontroller, and a plurality of microchips containing the external data processing and storage devices which are not integrated into the microcontroller. A microcontroller-based system of this kind comprises, for example, one or more printed circuit boards on which the microcontroller and the other components are mounted.
It is the application program, I. e. the program which is executed by the microcontroller, which determines the overall operation of the microcontroller system. Each application program is therefore specific to a separate application.
In most current applications the application program is too large to be held in the microcontroller and is therefore stored in a memory external to the microcontroller. This program memory, which has only to be read, not written, is generally a reprogrammable read only memory (REPROM).
After the application program has been programmed in memory and then started in order to be executed by the microcontroller, the microcontroller system may not function as expected.
In the last unfavorable situation this is a minor dysfunction of the system and the microcontroller is still able to dialog with a test station via a serial or parallel interface. This test station is then able to determin the nature of the problem and indicates precisely the type of correction (software and physical) to be applied to the system for it to operate correctly.
Unfortunately, most dysfunctions of microcontroller-based system result in a total system lock-up, preventing any dialog with a test station. It is then impossible to determine the type of fault, i.e. whether it is a physical fault (in the microcontroller itself, in an external read only memory, in a peripheral device, on a bus, etc) or a software fault(i.e. an error in the application program).The troubleshooting technique usually employed in these cases of total lock-up is based on the use of sophisticated test devices requiring the application of probes to the pins of the various integrated circuits of the microcontroller-based system under test.
There are various problems associated with the use of such test devices for troubleshooting a microcontroller-based system. The probes used in these test devices are very fragile, difficult to apply because of the small size of the circuit and their close packing, and may not make good contact with the circuit.
Also, because of their high cost, these test devices are not mass produced. Consequently, faulty microcontroller-based systems can not be repaired immediately, wherever they happen to be located at the time, but must first be returned to a place where a test device is available. Troubleshooting a microcontroller-based system in this way is time-consuming, irksome and costly.
To avoid the need for direct action on the microcontroller-based system each time the application program executed by the microcontroller of the system is changed, it is standard practice to use a downloadable read only memory to store the application program, a loading program being written into a mask-programmed read only memory of the microcontroller. The mask-programmed read only memory of the microcontroller is integrated into the microcontroller and programmed once and for all during manufacture of the microcontroller.
To change the application program the microcontroller is reset by running the downloading program. This downloading program can then communicate with a workstation connected to the microcontroller by an appropriate transmission line, this workstation the new application program to be written into the microcontroller. The downloading program receives the new application program and loads it into a read only memory external to the microcontroller.
Although this solution avoids the need for direct action on the microcontroller-based system (which would entail removing from the system the reprogrammable read only memories containing the application program, writing into these memories the new application program using an appropriate programming device and then replacing them in the system), it nevertheless has a major drawback, namely specialization of the microcontroller during manufacture.
Each type of reprogrammable memory is associated with a different downloading program because the programming parameters (voltage to be applied, duration for which the voltage is to be applied) vary with the technology employed. The downloading program is written once and for all into the mask-programmed internal memory of the microcontroller and the latter is therefore restricted to using memory components of the type for which this downloading program was written. In other words, the microcontroller is not a standard component and this increases its cost of manufacture.
One object of the invention is to overcome these various drawbacks of the prior art. To be more precise, an object of the invention is to provide a microcontroller circuit which can verify quickly, simply, reliably and at low cost the operation of a system based on the microcontroller.
Another object of the invention is to provide a microcontroller integrated circuit which can accurately locate the defective component or components of a system using the microcontroller in the event of dysfunction of the system.
A further object of the invention is to provide a microcontroller integrated circuit which avoids the need for direct action on the microcontroller-based system to change the application program, whilst remaining standard as regards the type of memory component with which it can be used in a system.
带有只读存储器的单片机集成电路
单片机集成电路包含一个处理器内核，它至少通过一种数据处理或存储设备来交换数据。集成电路包含一个只读掩模程序存储器，其中像测试程序一样的通用程序能被单片机执行。这种通用程序具有将数据写到数据处理和、或存储设备的基本功能。写入功能用于装载程序。因为装载程序并非永久地存储在只读存储器中，所以可对单片机进行测试，而与应用程序无关，并保持系统中能用的存储器元件为标准类型。
准确地说，这项发明涉及单片机集成电路。单片机通常是包含一台“计算机”的全部或大部分元件的大规模集成电路，其功能不是预先确定的，而是取决于它执行的程序。
一台单片机必然包含一个含有命令时序发生器（即根据程序的指令分配各种控制信号到其他元件的装置）的处理器内核，一个算数逻辑单元（用来处理数据）和寄存器（即特殊的存储单元）。
然而，“计算机”的其他单元对单片机而言或是内部的，或是外部的。换言之，其他元件就集成到单片机或辅助电路中。
“计算机”的这些其他元件是数据处理或存储装置，例如包含待执行程序的只读或随机存储器、时钟和接口（串行或并行）。
基于单片机的系统通常包含一个含有单片机的芯片和许多含有外部数据处理和、或存储器的芯片，这些芯片没有集成在单片机中。例如，这种基于单片机的系统包含一个或多个印刷电路板，上面安装着单片机和其他元件。
决定单片机所有操作的是应用程序，即由单片机执行的程序。因此，每个应用程序都是针对特定的应用的。
在多数现实应用中，由于应用程序太大，单片机无法存储，因此就存储在单片机的外部存储器中。这种只读处而不能写入的程序存储器通常就是可编程只读存储器。
应用程序在写入到存储器中后就开始执行，以便由单片机来执行。单片机系统有可能不会像预期的那样工作。
在最不顺的情况下，这只是系统的小故障，单片机仍然能够通过串行或并行口与测试设备对话。测试设备就能够确定问题的性质，并准确的指出校正的类型（软件和硬件），将其应用到系统上，以便正确操作。
遗憾的是，基于单片机系统的多数故障导致整个系统死锁，阻止了任何与测试设备的对话。这样就不能确定错误类型时硬件错误（单片机本身，外部只读存储器、外围设备、总线等）还是软件错误（应用程序的错误）。在系统死锁的情况下，采用的故障分析方法通常是以使用精密仪器测试设备为基础，因而要求将探测仪连接到处于测试中的单片机系统的各种集成电路的管脚上。
采用测试设备对于单片机的系统进行故障诊断，其相关问题还有很多。由于电路体积小，布线密集，而测试设备中使用的探针容易损坏，用起来很麻烦，就可能与电路接触不好。
此外由于成本高，这些测试设备不是批量生产。结果，出故障的单片机系统就不能直接及时修复，不管它们此时安装在何处，首先必须送到有测试设备的地方。单片机系统的这种故障诊断即费时又麻烦，成本也高。
在改变系统中单片机执行的应用程序时，为了避免直接在单片机系统上进行操作，常规的做法是用可下载的只读存储器来存储应用程序，即写入到单片机掩模ROM中的装载程序。单片机的掩模ROM集成到单片机中，并在生产单片机时一次性编程写入。
为了改变应用程序，单片机通过运行装载程序而重置。这个装载程序能通过合适的传输线与连接到单片机的工作站通信，而工作站提供写入到单片机的新的应用程序。装载程序接收新的应用程序并存储到单片机的外部ROM中。
尽管这种方法避免了对单片机系统的直接操作（这需要从系统中取出包含应用程序的可编程只读存储器，并用合适的编程设备将新的应用程序写进存储器，然后换到系统中），但是它仍然有一个较大的缺点，即在生产中对单片机的特殊处理。
由于编程参数（编程电压，外加电压的持续时间等）随着采用的技术而变化，每一种可编程存储器以对应的装载程序密切相关。装载程序一次性写进单片机内部的掩模存储器中，存储器因而就限制为装载程序要写入的存储器类型。换而言之，单片机不是标准器件，这就增加了生产成本。
这一发明就是为了克服先前技术的各种缺点。准确的说，该发明的目的就是要提供一种单片机产品，以便快速、简单、可靠、低成本地验证单片机的操作。
这项发明的另一个目的是提供一种单片机芯片，在系统出现故障时，可以借助于单片机准确地定位系统中失效的器件。
这项发明的更高目的是提供一种单片机芯片，在系统中能使用的存储器为标准类型时，不用直接对单片机系统进行操作就可改变应用程序。
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