Abstract: This paper designs a system for communication between a PC and a Foundation Fieldbus (FF) smart pressure transmitter using the Foundation Fieldbus communication control chip FB3050 as the communication controller. This system enables autonomous communication between the host computer and the pressure transmitter on the fieldbus that conforms to the FF protocol. Keywords: FF Bus , Communication, FB3050, MSC1210 1. Introduction The Foundation Fieldbus (FF) system uses field devices with communication capabilities and control and measurement functions as nodes, interconnecting them into a network via a bus. Through the exchange of operating parameters and data between the instruments at each node, information sharing and various automated functions of the system are achieved, forming a network-integrated automation system. The FF bus, as the lowest-level communication network in the control field, can be connected to the factory management network through a communication interface card conforming to the FF bus protocol. This enables communication and integration between the operation and control information of the production site and the management and command information of the control room and office, forming a complete industrial control information network system. 2. Overall Design of the FF Pressure Measurement System This paper designs a complete FF pressure measurement system. It not only designs an intelligent pressure transmitter conforming to the FF protocol, but also an FF bus PC interface card to realize communication between the FF bus intelligent pressure transmitter and the host computer. These are connected by the FF bus in the system, forming a complete FF bus pressure measurement system. The specific system block diagram is shown in Figure 1: [align=center] Figure 1 Overall Block Diagram of FF Pressure Measurement System[/align] The working principle of this system is as follows: The FF bus intelligent pressure transmitter converts the measured pressure signal into a Foundation Fieldbus-compliant digital signal and transmits it to the FF bus. The FF bus signal is received by the FF bus PC interface card, which converts the received signal into a PC_ISA-compliant signal and then transmits it to the host PC via the PC_ISA bus. Correspondingly, the control signals from the host PC are transmitted to the FF intelligent pressure transmitter in a symmetrical manner to operate the transmitter. 3. Design of FF Bus Intelligent Pressure Transmitter The FF bus intelligent pressure transmitter mainly consists of three parts: sensor and input circuit, communication interface, and media access unit. The design of the communication interface is a key aspect. This section of the design utilizes the MSC1210 microprocessor with integrated 24-bit A/D converter from Texas Instruments (TI) and the Foundation Fieldbus Communication Control Chip FB3050 from SMAR to develop an FF intelligent pressure transmitter. This transmitter performs high-precision data acquisition and processing of liquid or gas pressure parameters and enables reliable all-digital data communication via the FF bus. [align=center] Figure 2: Schematic diagram of the FF bus intelligent pressure transmitter[/align] The specific structure and connection method of this section are shown in Figure 2. The working principle of this part is briefly described below. First, the pressure sensor, driven by a constant current source, acquires the pressure signal and transmits the acquired mV signal to the microprocessor for processing via a differential input channel composed of the analog input channels AIN0 and AIN1 of the MSC1210. The signal processed by the MSC1210 then communicates with the bus via the FB3050 and MAU. The communication interface design is the key and challenging aspect of this section. The specific design method is as follows: Since the FB3050's interface design has fully considered the interface with Intel series CPUs, the MSC1210's data address bus can be directly connected to the FB3050's data address bus. However, a high-level signal must be output to PI_MODE to indicate that an Intel series CPU is selected. The MSC1210 has a data/address multiplexed port P0, and the FB3050 also supports data/address multiplexing, so no external address latch circuit is needed. The specific connection method is as follows: P0.0 to P0.7 of the MSC1210 are connected to the FB3050's 8-bit CPU data bus PB_CDATA[0:7], and a high-level signal is output to the FB3050's PI_MUXON to indicate that an address/data composite bus is used. The MSC1210's address latch signal output pin ALE is connected to the FB3050's address latch signal input pin PI_CAS. The high 8 bits of the MSC1210 address bus output port P2 are connected to pins 15-8 of the 16-bit CPU address bus PI_ADDR of the FB3050. Since an address/data multiplexed bus is used, pins 7-0 of the FB3050's 16-bit CPU bus need to be connected to ground. The interrupt outputs of the FB3050 and the external interrupt inputs of the MSC1210 are both active low, so direct connection is sufficient to fulfill interrupt request requirements. The clock output signal of the MSC1210 can be directly used as the system clock input of the FB3050. The specific connection is shown in Figure 2. This solves the communication problem between the MSC1210 and the FB3050 for data and control information, thus completing the design of the communication interface. 4. Design of the FF Bus PC Interface Card Since the host PC and the FF fieldbus cannot be directly connected to achieve information exchange, an FF bus PC interface card must be designed to meet the communication requirements between them. Figure 3 shows a simplified design diagram of this section, which mainly consists of four parts: a dual-port RAM chip IDT7142, a microcontroller INTEL80188, a communication control chip FB3050, and a media access sublayer. This design uses the INTEL80188 CPU, the most common CPU in embedded control, as the CPU on the interface card. The INTEL80188 provides 20 address lines, a 1MB memory address space, and a maximum I/O address space of 64KB (16-bit address lines). It also integrates an interrupt controller, two DMA controllers, three 16-bit timers, six programmable memory chip select lines, and seven programmable I/O interface chip select lines, making the design of embedded control circuitry very convenient. The communication between the interface card CPU and the PC CPU uses a dual-port RAM method, as this method allows for data block-level synchronization between the two CPUs. 5. Design of the Media Access Unit The Media Access Unit (MAU) is a crucial component for normal communication between the FF intelligent pressure transmitter and the host PC. Its function is to send and receive physical signals conforming to the FF specification. The FF bus signal receiving section works as follows: the FF bus signal is transmitted through a three-winding transformer to a 10-40kHz bandpass filter composed of operational amplifiers OP439 for filtering. The processed signal is then sent to a voltage comparator composed of operational amplifiers OP942 for signal shaping. The comparator outputs a relatively clean digital signal to the PI_PHPDU pin of the FB3050, thus completing the reception of the FF bus signal. Signals to be transmitted are sent to the FF bus via a bus driven by four 74HC126 differential drivers. Four 74HC126s are divided into two groups. The inputs of the two 74HC126s in each group are connected together. Then, the inputs of the two groups are connected by an inverter and then connected to the PO_PHPDU pin of the FB3050. The enable pins of all four 74HC126s are connected together and then connected to the PO_TACT control signal of the FB3050. Also, capacitors C1 and C2 in Figure 4 are used for DC blocking, R1 and C3 form a terminating matching circuit, and R9 and R10 are current-limiting resistors. [align=center] Figure 4 Simplified diagram of MAU[/align] 6. System Software Design The software design of this system mainly consists of two parts with the same design concept: the communication system software design between the host PC and the Foundation fieldbus, and the communication system software design between the FF intelligent pressure transmitter and the Foundation fieldbus. Here, I will use the communication system software design between the host PC and the Foundation fieldbus as an example to illustrate the software design of this system. The main design idea of ​​this section is as follows: When there is a signal on the fieldbus, the signal is first received by the FB3050 through the media access unit and transmitted to the receive buffer on the PC interface card. Then, it is selected by the INTEL80188 and transmitted to the PC application for processing through the PC_ISA bus interface. Conversely, when the host PC needs to send control information, it is sent in the opposite way. A simplified software design diagram is shown in Figure 5. [align=center] Figure 5 PC and FF communication software design diagram[/align] 7. Conclusion With the increasing maturity of various fieldbus technologies, their applications are becoming more widespread, and the DCS currently in use will gradually be replaced by FCS. As one of the more influential bus protocols, the FF bus highlights its advantages, so measurement systems based on FF bus technology will become increasingly popular, making research in this area very valuable. The innovation of this paper lies in integrating the FF fieldbus protocol specification into the design of the instrument, realizing the all-digital communication between the pressure transmitter on the bus and the upper control computer, replacing the existence of analog signals in some other buses, reducing the probability of interference, greatly improving the reliability of transmission on the bus, and making the whole pressure measurement system adaptable to more severe measurement environments, which has great practical significance. References: [1] Tang Huiqiang. Development of precision pressure transmitter. Measurement and control technology, 1999, 6-18: 63-64. [2] Sun Zhanhui, Zhang Peiren, et al. Application of CAN bus in fieldbus control system. Microcomputer information, 2002, 7: 7-8. [3] Yang Xianhui. Fieldbus technology and its application, 1st edition, Beijing: Tsinghua University Press, 1999: 138-141 [4] Deng Hongbin. 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