A study of the BLC-80/11A microcomputer card

Abstract

At the beginning of the academic year 1982-83 the Electrical Engineering Department at the University received a set of microcomputer cards each containing the basic elements of hardware required to set up a complete microcomputer system. These basic elements essentially consisted of: a microprocessor serial and parallel 1/0 blocks a memory section consisting of some RAM with provision for more and facilities for ROM, although none was actually present on card Needless to say, also contained in these cards were all the relevant logic circuits necessary for the proper operation of the hardware. The scope of the project was to evaluate the possibilities of one of these cards and possibly to activate one of them. One of these cards was the BLG - 80/IIA which is based on the INS 8080A N channel LSI microprocessor. A schematic diagram is shown in figure I. The card as it stood did not contain a monitor and as such it could not be operated in any way as for example with a keyboard and display system. Thus, the first step was to provide the card with an operating system. An operating system can be defined as a set of rules that have to b€ followed to make a system carry out a job. The same term is also used to denote that part of the control program concerned with getting programs running and controlling them while they are running. In turn the control program is an extensive program which controls the operations of the several other routines necessary for operating the hardware. It will include for example all subroutines dealing with peripheral devices, not only the subroutines that call them into operation but also the subroutines that perform the operations that are necessary after a transfer has been completed. The control program is also referred to under different names by different systems such as monitor, supervisor, executive etc. In this text it shall be referred to as the system monitor. Once the operating system is formulated according to the needs of the job to which the hardware is to be put, there remains one basic problem. The ROM is initially devoid of any control program. So, a program is required that will "lift itself" or to use the exact expression "load itself" into memory. This program is called a Boostrap program. It is a relatively short program to be loaded into memory from an external device. The starting point of the project was therefore to design a Bootstrap program with the ai~ of being able to utilize the BLC-80/IIA card. The program was developed on the Elettronica Veneta microcomputer development system. This was the only suitable development system available in the laboratory, since it is based on the 8085 microprocessor. The 8085 microprocessor is very similar to, the 8080 microprocessor and uses the same interface circuitry. The 8085 is an improved version of the 8080 microprocessor with some additional features. Since the scope was to develop a loader, under control of which information from an input device is taken into the system and placed in specific locations of memory, there arose the need for another input system and hence another interface system. How this was se~ up and how it was used in conjunction with the present system i.e. the Elettronica Veneta, shall be described in Chapter 2. -Once the loader was developed, it was envisaged that it would be adapted for use with a keyboard and display system such that the microcomputer card would have been developed into another complete microcomputer system. Furthermore, with the aid of the expansion facilities of the card itself, it could in future be used for several purposes, when desired. Several problems were encountered, mainly with the unavailability of components and literature on time. The interface circuit required was, and still is at the time of writing, unavailable at the Electrical Engineering Department. Furthermore, no literature was available on time as were neither the edge connectors. Both arrived in mid-March 1983. In spite of these difficulties, the project still gave scope for acquiring knowledge and gaining practical experience in microcomputer systems in particular with the Intel 8080 and 8085 systems.