Software and hardware design of temperature recorder system based on ferroelectric memory

1 Introduction

The high temperature tester is mainly used for temperature tracking measurement and data collection during the heating process. Through systematic analysis of the test data, the temperature distribution and temperature difference changes in the furnace are studied, the main factors affecting the heating quality are analyzed, and the heating process of the heating furnace and The heating system is optimized to improve heating quality and reduce fuel consumption.

In some systems that collect and store data, the system voltage may fluctuate or suddenly lose power. FM20L08 is a memory designed for these systems that can be used to directly replace asynchronous static memory (SRAM). It is also Ramtron's largest capacity iron memory. Electrical memory (FRAM), capable of unlimited read and write operations. Using FM20L08 can greatly save circuit board space. The temperature tester using FM20L08 memory has the characteristics of large-capacity data storage, impact resistance, anti-interference, no data loss when power is off, and high real-time acquisition speed.

2. Ferroelectric memory (FRAM) and FM20L08

2.1 Introduction to Ferroelectric Memory

FRAM is a power-down non-volatile memory launched by Ramtron in recent years. It combines high performance and low power consumption operation and can save data without power supply. The core technology of FRAM memory technology is ferroelectric crystal material. This special material allows ferroelectric memory products to have the characteristics of random access memory (RAM) and non-volatile memory products. The working principle of ferroelectric crystal materials is: when an electric field is applied to ferroelectric crystal materials, the central atoms in the crystal array will move along the direction of the electric field and reach a stable state. Each free-floating central atom in the crystal array has only two stable states. One is used to remember 0 in logic, and the other is used to remember 1. The central atom can stay in this state for more than a hundred years at room temperature and without an electric field. Ferroelectric memory does not need to be refreshed regularly and can save data during power outages. Since there are no atomic collisions in the entire physical process, FRAM has super features such as high-speed reading and writing, ultra-low power consumption, and unlimited writes.

2.2 FM20L08 features and pin functions

FM20L08 is a FRAM with a storage capacity of 128×8bits launched by Ramtron in recent years. Its read and write operations are the same as standard SRAM. The main features are as follows: 3.3V single power supply; parallel interface; available in SOIC and DIP packages; low power consumption, quiescent current less than 10μA, read and write current less than 15mA; non-volatile, data can be saved for 10 years after power failure; access Entry time is 60 ns. The high-speed page mode operation bus speed can reach up to 33MHz, 4-byte pulse; there is no delay in writing operations, and unlimited reading and writing times; it can meet industrial temperatures (-40℃ to +85℃).

The pin arrangement of FM20L08 is shown in Figure 1. The functions of each pin are as follows:

CE1/CE2: chip select terminal;

WE: write enable terminal;

OE: output enable port;

A0～A16: address side;

DQ0～DQ7: data terminal;

VDD: power supply;

VSS: Ground terminal.

Figure 1 FM20L08 pin diagram

Figure 2 Principle block diagram of temperature recorder

3. Hardware composition of temperature recorder system

A 16-bit microcontroller CPU containing multiple switches, A/D converters, and voltage reference sources is used to form a 16-channel low-power temperature recorder [2]. The filter circuit composed of RC filters out the interference signal in the thermocouple signal, and is input to the operational amplifier through the eight-select one multi-channel switch to amplify it to an appropriate level, and then input to the CPU for A/D sampling, and is stored after numerical conversion and linearization. stored in FRAM memory. After the entire measurement is completed, the communication interface is connected to the PC and the data is transmitted to the PC for further analysis and processing. The power supply part is composed of a low-power consumption low-voltage voltage stabilizing circuit and a filter circuit. The system provides a 3.3 V working power supply. All components of the temperature recorder are of industrial grade, allowing the operating temperature to operate normally between - 45 and 85 ℃. Figure 2 is the schematic block diagram of the temperature recorder.

FM20L08FRAM is different from general SRAM in use. FM20L08 is selected when CE2 is low and high, and each access must ensure a transition from high to low. Because the technology used in ferroelectric memory is relatively special, there is a precharge process during operation. The precharge operation is an internal condition for newly accessed memory. All memory cycles include memory access and precharge. Precharge is started by the pin being high. It must remain high for at least a specific minimum time.

4. Temperature recorder system software design

The program is divided into main program, data acquisition program, and USB communication program [3]. The working process is: the recorder first applies voltage and is interrupted by an external signal, so that the microcontroller enters the subroutine of data collection and loops. After reaching the timing time, it stops collecting, exits the subroutine, enters the main loop, and waits for the external trigger of the serial port signal, thus Enter the data transmission subroutine and send the data to the PC through the serial port. Figure 3 is the temperature recorder program flow chart.

Figure 3 Temperature recorder program flow chart

5. Anti-interference measures

5.1 Hardware anti-interference

In order to prevent misoperation of AD from erasing the data in the memory after the recorder is recycled and powered on again, consideration should be given to eliminating this possibility from the hardware design. The most fundamental method is to disconnect the data from the acquisition module from the hardware. connect.

5.2 Software anti-interference

When the microcontroller is affected by interference signals, the system will be out of control. The most typical one is the status value of the PC. Its modification will lead to two main forms of abnormal software operation: "program runaway" and "infinite loop". To this end, three anti-interference methods are adopted in the design: (1) Instruction redundancy technology. Instructions are composed of opcodes and operands. The opcode specifies what kind of operation the CPU wants to complete, and the operand is the object of the opcode. Single-byte instructions only have opcodes and implicit operands; double-byte instructions, the first byte is the opcode and the second byte is the operand; three-byte instructions have the first byte is the opcode, followed by The two bytes are operands. When the CPU fetches instructions, it first fetches the opcode and then the operand. How to determine whether it is an opcode or an operand is based on the order of fetching instructions. The order of fetching instructions is completely controlled by the instruction counter PC. Therefore, once the PC is disturbed and an error occurs, the program will deviate from the normal track and "fly around". In this way, the operands will be regarded as opcodes, or the opcodes will be used. as an operand. But as long as the PC pointer falls on a single-byte instruction, the program can be put on track. Therefore, in order to quickly put the program on track, you should use more single-byte instructions, and artificially insert some single-byte instruction NOPs in key places, or replace the valid ones with Single-byte instructions are rewritten, which is called instruction redundancy. A common method is to insert two single-byte instructions NOP after some double-byte or three-byte instructions, or insert two NOP instructions before some instructions that determine the flow of the program. Some important instructions can also be placed repeatedly. However, the condition for using instruction redundancy technology to put the program on track is: the flying PC must point to the program running area. (2) Watchdog technology [4]. Dedicated hardware watchdog refers to some dedicated watchdog circuits that are integrated or integrated in a microcontroller. In fact, it is a special timer that emits an overflow pulse when the timer expires. From an implementation perspective, this method is a technology that combines software with external dedicated circuits. After the hardware circuit is connected, some watchdog reset instructions are appropriately inserted into the program to ensure that the watchdog does not overflow when the program is running normally. ; When the program runs abnormally, the watchdog times out and issues an overflow pulse, and resets the microcontroller through the RESET pin of the microcontroller. (3) Software trap technology. When a flying program enters a non-program area, a software trap can be set to intercept the flying program and lead the program to a fixed location. This allows the captured program to be put back on track. The main purpose of software trap is to reintroduce the program to its reset entry, that is to say, set such instructions in the appropriate place:

NOP

NOP

LJMP 0000H

Software traps are mainly arranged in the following areas: unused interrupt area, unused EPROM space and non-EPROM space, program running area and interrupt service program area.

5 Conclusion

As a new generation of non-volatile memory, ferroelectric memory can be well guaranteed in terms of writing speed and data security. It has been widely used in various industries such as foreign subway systems, meter reading systems and IT. Applications. The temperature recorder designed in this article not only has the characteristics of resisting overload impact, resisting interference, and not losing data when power is turned off, but also has the characteristics of high real-time acquisition speed and large storage capacity. Its practical application has military and commercial value and can obtain high economic benefits.