DE29821808U1 - Electronic device, in particular field device - Google Patents

Description

GR 98 G 4458 EN

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1
Description

Electronic device, especially field device

The invention relates to an electronic device, in particular a field device according to the preamble of claim 1.

In electronic devices that are equipped with a microprocessor for executing a user program, data that is determined dynamically during operation must often be available even after a voltage drop when the device is restarted. Non-volatile storage media, e.g. Flash EPROM*s or EEPROM^s, are used for storage. In the event of a voltage drop, the data that was previously usually held in a memory for temporary data must be transferred by the processor to the non-volatile memory. To do this, a so-called power fail detector, which detects a drop in the supply voltage at an early stage, initiates an interrupt routine with the steps required to save the data. An energy storage device provides the energy required to save the data in the non-volatile memory. A suitable non-volatile memory is, for example, the 1 K x 8 bit EEPROM X25080 from Xicor, which has a 32-byte page mode for writing to the memory cells. In the first phase of a write cycle, a data packet, a so-called page, is transmitted via a serial interface, the so-called Serial Peripheral Interface (SPI). This process is comparatively fast, as it takes place at a transmission rate of 2 megabits per second. In a second phase of the write cycle, the EEPROM automatically stores the data in the assigned non-volatile memory cells. The EEPROM requires a maximum of 10 ms for this. Only after this time can another write cycle be carried out. In order to ensure that a maximum of one page of data is saved in the event of a voltage drop, it is sufficient to use backup capacitors.

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to provide enough energy for the microprocessor and memory in the first phase and for just the EEPROM in the second phase. However, the amount of data is then limited by the page size.
5

The invention is based on the object of creating an electronic device, in particular a field device, which allows the backup of a data volume larger than one page after a power failure and which nevertheless manages with a comparatively small energy storage device.

To achieve this object, the new electronic device of the type mentioned at the outset has the features specified in the characterizing part of claim 1. Claim 2 describes an advantageous embodiment of the invention.

The invention has the advantage that larger energy storage devices, such as buffer capacitors, are not required. The dimensioning of electrical energy storage devices is particularly critical for intrinsically safe field devices. In addition, the currents and voltages permitted in the event of a fault are subject to strict regulations and must be limited, for example, by resistors or Zener diodes.

Microprocessors that can be switched to an energy-saving mode have a significantly lower power consumption in this operating mode. The type Cl65 from Siemens requires approx. 26 mA of supply current at a clock frequency of 4 MHz. In contrast, the supply current in idle mode is reduced to approx.

6.8 mA, in power-down mode even up to 100 μα. In energy-saving mode, only a small amount of energy storage capacity is required to supply the microprocessor. After the second phase, the microprocessor is returned to normal operation in order to transfer another page to the non-volatile memory. The invention thus makes it possible to save larger amounts of data after a power failure.

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Alternatively, EEPROMs with smaller pages or even byte-by-byte transfer can be used. The manufacturer of the electronic device is not forced to use expensive EEPROMs that have a page large enough to store the desired amount of data. This can reduce the manufacturing effort.

With reference to the drawing, in which an embodiment of the invention is shown, embodiments and advantages of the invention are explained in more detail below.

The drawing shows a pressure transmitter 1 as an example of an electronic device in which data is stored in a non-volatile memory after a power failure.

A field bus 2 is used for communication and to supply operating energy. This is connected to a bus interface 3 with power supply integrated in the pressure transmitter 1. The measuring pressure is fed to a measuring device 5 via a pressure line 4. In the measuring device 5, the pressure signals are converted into a form suitable for a microprocessor 6. The microprocessor 6 executes a user program which is stored in a memory 7 designed as a ROM. Dynamic data, e.g. parameters of the measuring program, calibration parameters, diagnostic data, operating hour counters and the like, are kept in a RAM memory 8. The microprocessor 6, ROM memory 7, RAM memory 8 and bus interface 3 are connected to one another for communication by an internal bus 9 which includes address, data and control lines. Some of the dynamic data, in particular data for diagnostics and quality assurance, should also be retained after a power failure. Particular mention should be made here of data which permit an assessment of the status of the field device on the basis of operating conditions, e.g. B. the reading of an operating hour counter or the information whether the measuring range or the permissible ambient temperature

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were exceeded. It is easy to check whether a sensor overload has occurred in the pressure transmitter 1 by storing the highest and lowest measured pressure values. In order to save this data even in the event of a power failure, a non-volatile memory 10 is provided, in this case an EEPROM of type X25080 from Xicor, which is connected to the microprocessor 6, in this case a C165 from Siemens, via an SPI interface 11.

The data to be backed up is managed dynamically during operation of the field device and temporarily stored in RAM memory 8. In principle, it would be sufficient to back up the data by writing it to non-volatile memory 10 shortly before the field device is switched off. However, since a voltage drop can be caused unexpectedly, for example by a break in the field bus line 2, saving would have to take place at short intervals in order to have the most up-to-date data backed up. However, this would have the disadvantage that the saving processes would require additional time and energy. In particular, energy is only available to a very limited extent in field devices that are remotely powered via a field bus. In order to save energy, microprocessors are usually operated at the lowest possible clock rate. Therefore, little microprocessor power is left for data backup tasks in addition to processing the actual application program. In addition, non-volatile memories, especially EEPROMs, cannot be written to as often as desired, so that regular backups of data at short intervals would have significant disadvantages.

A better way to back up data is to provide an energy storage device 15 that, after a voltage drop, maintains the operating voltage of the components involved for the time required to back up the data. A power fail detector 11 sends a signal 12 to the microcontroller to indicate a voltage drop.

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processor 6. Such a power fail detector can alternatively be integrated in the power supply of the bus connection 3. The signal 12 is fed to an interrupt input of the microprocessor 6 and starts an interrupt routine in which the data to be saved is transferred to the EEPROM 10. Furthermore, the current status in the RAM memory 8 is stored in the interrupt routine in order to record which data has already been saved. The microprocessor 6 starts a timer 13 and is then switched to an energy-saving mode by a software command. While the microprocessor 6 is in energy-saving mode, the non-volatile memory 10 stores the data received with the first page in the assigned non-volatile memory cells. This takes a maximum of 10 ms. Other peripheral components that are not addressed by the microprocessor 6 in energy-saving mode require only a small amount of power. After 10 ms have elapsed, the timer 13 returns the microprocessor 6 to normal operation. For this purpose, a signal 14 is connected to an interrupt input. In the interrupt routine, the microprocessor 6 reads the status that was saved before the last energy-saving mode and continues the data backup from this point. The second page is now transferred to the non-volatile memory 10 and then the microprocessor 6 is returned to energy-saving mode in the manner described. This process is repeated until all data has been saved, i.e. a third, a fourth and possibly further pages have been written.

Since the microprocessor 6 only operates in normal operation during the first phase of the write cycles for transferring the data to be backed up to the non-volatile memory 10 and is in energy-saving mode during the second phase, which is considerably longer, the majority of the capacity of the energy storage device 15 is required for the supply current of the non-volatile memory 10 during data backup.

Claims (2)

1. Electronic device, in particular field device, 1. with a microprocessor ( 6 ) for executing an application program, 2. with a memory ( 7 ) in which the user program can be stored, 3. with a memory ( 8 ) in which temporary data can be stored, 4. with a non-volatile memory ( 10 ) in which at least part of the temporary data can be stored for backup in the event of a power failure, wherein in a first phase a data packet, a so-called page, can be transferred to the non-volatile memory ( 10 ) and the non-volatile memory ( 10 ) is designed to store the data packet independently in the associated non-volatile memory cells in a second phase, and 5. with an energy storage device ( 15 ) through which the energy required to save the data can be provided after a power failure, characterized , 1. that the microprocessor ( 6 ) can be switched to an energy saving mode in which the energy consumption is significantly lower than in normal operation, and 2. that means are provided to switch the microprocessor ( 6 ) into energy saving mode after the first phase has ended in the event of a power failure and to return the microprocessor ( 6 ) to normal operation after the second phase has ended. 2. Electronic device according to claim 1, characterized in that a timer ( 13 ) is provided which is started by the microprocessor ( 6 ) after the first phase and which, after the expiration of a time which is at least greater than the duration of the second phase, returns the microprocessor to normal operation.