Design and application of interface conversion based on single chip microcomputer

3 Interface conversion software design
Because of the large-scale integrated circuit interface chip, the hardware implementation of the interface conversion circuit board is relatively easy. The key is to design a complete supervision and management program. The program flow chart is shown in Figure 2. The process design is based on GPIB transmitting data to RS232C. Therefore, after the monitoring system is initialized, it first identifies whether MC68488 is listening to the command? Once it is listening to the command, it receives GPIB data until a data block is input. After the data block is input, the Intel8251 data transmission part is started, and the data bytes input from MC68488 are continuously sent. RS232C receives data from identifying the Intel8251 receiving interrupt. If the Intel8251 status register D7 = 1, the supervision program will enter the branch of receiving data from RS232C. First, the entire data block is received from Intel8251, and then a service request is made to the GPIB controller with the help of the SRQ line of GPIB; after the GPIB controller executes the serial query sequence and responds to the converter service request, the received data block can be output to the listening device (or controller) of the GPIB system through MC68488. Note that when receiving a data block from RS232C, the last byte identification mark must be agreed upon.
4 Interface conversion application examples
PCB program-controlled probe positioning equipment is a device that locates the test point of the tested printed circuit board. With the support of a computer, it automatically locates at the tested point and penetrates the protective layer of the printed circuit board to obtain the electrical signal of the tested point. Its composition structure is shown in Figure 3. Its positioning function is realized by the system main controller through the GPIB bus, and the power supply, signal source and test instrument of the PCB are determined by the characteristics of the specific PCB under test. The program-controlled probe positioning equipment uses stepper motor open-loop control to realize the free movement of the probe in the X and Y directions, and uses electromagnet suction control to realize the up and down movement of the probe. The probe penetrates the PCB solder mask layer by scratching to maintain reliable contact with the test point. The microprocessor circuit board of the positioning equipment is an outsourced product, which can realize the control of the stepper motor displacement and electromagnet suction. In addition, the RS232C interface has been designed in the microprocessor circuit board, which can realize serial communication with the main control computer of the test system. However, in ATS, GPIB control is usually used for program-controlled desktop test equipment, so GPIB-RS232C interface conversion is required. The interface conversion circuit designed by the above method can ensure that the PCB program-controlled probe positioning device is connected to the GPIB bus and smoothly connected to the ATS. In addition, in addition to using the GPIB interface, the program-controlled signal can directly use the RS232C control method to complete all functions of the PCB program-controlled probe positioning device by unplugging the RS232C plug connected to the interface conversion circuit board with an external cable, and the GPIB control is invalid at this time.

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