Abstract: A Chinese fire indicator using a large-capacity FLASH memory to store floor address information is proposed. This device analyzes information from the fire alarm controller through the CAN bus and dynamically displays the location and type of the fire on a Chinese LCD module in real time. The software and hardware architecture of the fire indicator in the fire alarm system is introduced in detail. Keywords : Fire alarm; CAN bus; Fire indicator; FLASH; Chinese LCD 1 Introduction The fire floor indicator, as an important component of the automatic fire alarm system, is a digital fire alarm display device installed on floors or in independent fire zones. It is connected to the fire alarm controller through the alarm bus, processing and displaying the data on the alarm bus. The built-in microcontroller in the fire alarm floor display judges, analyzes, and processes the received bus information, converting the alarm detector address number into the corresponding fire alarm location information (such as room number and room type), and displays it along with the fire alarm type on the LCD. Simultaneously, it emits audible and visual alarm signals to notify personnel in the fire area. Currently, most existing fire alarm floor displays in China use the 51 microcontroller as the MCU. Due to ROM address space limitations, most fire alarm floor displays can only display the floor number and address of the fire, and cannot intuitively indicate the specific fire location with different Chinese characters. If Chinese character information is distributed to each floor display via the bus, the huge communication volume will place a heavy load on the fire alarm system bus, leading to low efficiency of the entire fire alarm system and delays in fire alarm reporting. This paper proposes a high-capacity Chinese character fire alarm floor display based on the CAN bus, which effectively solves the above problems. 2. Overall Functional Description of the Fire Alarm System In the fire alarm control system, the central fire alarm controller communicates with each unit in real time via the CAN bus and completes various control and alarm functions. A unit is a general term for devices such as fire detectors, manual alarm buttons, input/output modules, and floor displays. These are system terminals that directly detect fire signals and report them to the controller via channels. They also receive linkage information (activating fire extinguishing devices controlled by input/output modules) and display information (displaying fire information on floor displays) from the controller to the units via various channels. A channel is a general term for devices such as loop modules, transfer modules, and bus control panels. They are channels between control devices and terminals, and are relay devices in the topology network. The overall structure of the fire alarm control system and the location of the floor displays in the system are shown in Figure 1. [align=center] Figure 1 Fire Alarm Control System Structure and Location of Floor Displays[/align] 3 System Functions and Hardware Description 3.1 Hardware Design Scheme for Chinese Character Floor Displays As shown in Figure 2, the Chinese character floor display includes a microcontroller and its peripheral circuits, a CAN bus module, a FLASH memory, a Chinese character LCD module, a UART interface, as well as lights, buttons, and a buzzer. The microcontroller can receive Chinese character information uploaded from the PC via UART and store it in the FLASH memory as a database for address information lookup. The CAN communication module, consisting of a CAN controller MCP2510 and a CAN bus driver PCA82C250, communicates with the fire alarm controller via the CAN bus. If a fire alarm occurs, the microcontroller records the alarm information, queries the FLASH memory to obtain the Chinese character address information of the fire alarm, and displays the fire alarm and information query results on the Chinese character LCD screen. Simultaneously, during a fire alarm, the system can quickly query the fire alarm information using the query key, sound an alarm via a buzzer, silence the alarm via a mute key, and illuminate an LED as an alarm. When no fire alarm occurs, a self-test key can be used to check if each function is working properly. [align=center] Figure 2: Block diagram of the Chinese character floor display[/align] 3.2 FLASH memory circuit design The selected FLASH memory is the SST29SF040, a high-speed programmable flash memory from SST Corporation. It conforms to the JEDEC standard and features a 512K×8-bit memory structure. The chip boasts fast erase and write times: a full erase takes only 70 milliseconds, a segment erase only 18 milliseconds, and a word programming write time of just 14 microseconds. It also offers high reliability, capable of being rewritten 100,000 times and retaining data for 100 years without loss. The SST29SF040 has a capacity of 512K bytes, while the ROM direct addressing range of the 51 series microcontroller is 64K bytes. Using this directly without processing would waste a significant amount of storage space. We employed a paging storage method, which fully utilizes the FLASH storage space and greatly expands the microcontroller's ROM addressing range. Based on each Chinese character occupying 32 bytes, it can theoretically store a maximum of 16,384 fire alarm address entries, sufficient to handle most complex engineering environments. Figure 3 shows the memory circuit. The highest address lines A16-A18 are connected to P1.0-P1.2 of the microcontroller, thus the FLASH memory implements an external storage structure of 8 pages, each page being 64K. Different page selections can be achieved by assigning different values ​​to P1.0-P1.2 each time the FLASH is read or written. Assuming page is the page number variable to be selected (0-7), the page selection operation before reading or writing can be achieved in Keil Cx51 using the following statement: P1 = (P1 & 0xf8) | page; [align=center] Figure 3 FLASH memory paging circuit[/align] 3.3 Design of Chinese character LCD display module We selected the OJM2*8A Chinese character LCD module from Jinpeng Electronics as the display device. The OJM2*8A Chinese LCD module contains 15*15 dot matrix GB 2312 simplified Chinese characters (levels 1 and 2) and 8*8 and 8*16 dot matrix ASCII characters. Users can input GB2312 zone codes or ASCII codes to display text. Each Chinese character's zone code occupies only two bytes, which is 1/16 of the storage unit required by the original Chinese character dot matrix. The interface protocol of the Chinese LCD module is a request/response (REQ/BUSY) handshake. A high level BUSY signal (BUSY = 1) indicates that the LCD module is busy with internal processing and cannot receive user commands; a low level BUSY signal (BUSY = 0) indicates that the LCD module is idle and waiting to receive user commands. Sending commands to the LCD module can begin at any time after BUSY = 0. First, the current byte of the user command is placed on the data line, followed by a high-level REQ signal (REQ = 1) to notify the LCD module to process the command or data on the current data line. Upon receiving an external REQ high-level signal, the LCD module immediately reads the command or data on the data line and simultaneously sets the BUSY response line high, indicating that the module has received the data and is busy processing it internally. At this point, the user's write operation to the module is complete. The user can cancel the signals on the data line and perform other tasks besides displaying the data. The user can also continuously check if the BUSY response line is low (BUSY=0). If BUSY=0, it indicates that the module has completed the write operation and can send the next data. For example, sending a complete command to display a Chinese character requires 5 bytes, including coordinates and the character code. The module only begins executing the entire command's internal operations after receiving the last byte; therefore, the BUSY response (BUSY=1) for the last byte is high for a relatively long duration. The timing diagram for writing Chinese characters to the LCD module is shown in Figure 4. [align=center]Figure 4 Timing Diagram for Writing Chinese Characters to the LCD Module[/align] 3.4 CAN Bus Communication Module Design We chose Microchip's MCP2510 CAN controller and Philips' PCA82C250 CAN transceiver to build the CAN bus communication module. The MCP2510 supports the CAN 2.0A/B protocol and can receive and send standard frames, extended frames, and remote frames under the 2.0 protocol. The MCP2510 has three transmit buffers and two receive buffers, which can perform receive filtering and message management to prevent congestion caused by over-transmission and over-reception. Its biggest advantage is that it has an SPI port with a transmission rate of up to 5Mb/s, saving MCU ports and improving communication speed. Philips' 82C250 CAN bus transceiver can be seamlessly connected to the MPC2510. It has high-speed mode, slope control mode, and delay mode. After many experiments, it was confirmed that it works most stably in slope control mode, and the speed can meet the system's 10Kbps transmission rate. [align=center]Figure 5 CAN Bus Communication Circuit[/align] The CAN bus communication module circuit is shown in Figure 5. The microcontroller is directly connected to the SPI port of the MCP2510 through the I/O port, and the SPI interface protocol is simulated by software. The PCA82C250 serves as the interface between the MCP2510 and the physical CAN bus. If it is necessary to further improve the anti-interference capability of the system, an opto-isolator can be added between the MCP2510 and the PCA82C250. 4 System Software Design The main functions of the Chinese character floor display software are: 1. Write the Chinese character information file sent from the serial port into the FLASH storage. 2. Communicate with the fire alarm controller via CAN. If a fire alarm is detected, the address information of the Chinese character in the FLASH is searched and displayed on the Chinese character LCD. If there are multiple fire alarm messages, each message is displayed in a scrolling manner. [align=center]Figure 6 Flowchart of the Chinese Character Floor Display Software[/align] Figure 6 is the flowchart of the Chinese character floor display software. Page (value 0-7) represents the FLASH page to be read and written, and count (value 0-65535) represents the address within each page. Pages 0-6 are used to store Chinese character information downloaded via serial port, and page 7 is used to store received dynamic information such as fire alarms. Once a new fire alarm is received, the corresponding Chinese character information in the FLASH is queried and displayed on the LCD. To quickly locate the queried fire alarm Chinese character address information, we use an array structure for storage. Although this may result in some empty addresses in storage due to the varying lengths of actual fire alarm addresses, leading to lower storage efficiency, the array search is a direct and fast search method, avoiding complex data structures like linked lists and complex search algorithms like binary search. For the microcontroller, this trade-off of relatively small space for higher time efficiency is well worth it. 5 Conclusion The large-capacity Chinese character fire floor display based on the CAN bus proposed in this paper effectively solves the shortcomings of existing fire floor displays. For data storage requirements of more than 51 microcontroller ROM 64K address space, the paging storage access method can solve this problem well. By storing large amount of data information in FLASH, it is possible to avoid the fire alarm not being transmitted in time due to the large amount of communication data flow on the CAN bus, thus delaying the alarm timing. Moreover, the Chinese character information in FLASH can be erased and written online through the serial port, which is convenient for on-site debugging. The product has been put into practical use and users have reported that it is running well. References [1] Zhu Ming, Wang Shu. Design and implementation of a lower-level network for a large fire alarm system based on CAN bus. Fire Protection Technology and Product Information, 2003, (12): 5-8 [2] Wang Lifeng, Wang Xiaoping, Geng Qingbo, Peng Xiwei. Design of guest room communication controller based on CAN bus. Microcomputer Information, 2005, (16): 3-7 [3] Xu Aijun, Peng Xiuhua. Keil Cx51 V7.0 microcontroller advanced language programming and uVision2 application practice. Electronic Industry Press, 2004