ADuC812 MicroConverter

A Microcontroller

Dedicated For

Control Applications

 S Gupta

 

Summary

This article presents the new highly integrated microcontroller ADuC812 from Analog Devices Some of the unique features of this microcontroller are highlighted.

 

 

 

ADuC 812 Flash Microcontroller

ADuc812 microcontroller comes very close to what a control engineer may dream of. It targets instrumentation and measurement control applications, including the implemention of IEEE 1451.2 interface. This interface is gaining momentum for smart transducer interface, where a device such as ADcU812 is used for maintaining transducer electronic data sheet (TEDS). Furthermore, the device can be completely erased and reprogrammed if necessary. It also contains data EEPROM to hold control coefficients and user constants. Consider the following features, some of which are not commonly found in microcontrollers.

 

Analog To Digital Converter

Digital To Analog Converter

 Flash Program Memory

Data EEPROM

Data RAM

Peripherals

Microcontroller Core

 

It is not only the features that are provided on the microconverter, which are impressive but also the functionality that is built into it. Specifications of ADC and DAC are impressive, but then one expects these from a company like Analog Devices. It is the well thought of integration into the microcontroller core that is quite significant.

 

It seems that the ADuC812 is designed not by design engineers,

 but by application engineers

Well Done.

(Micro Control Journal)

 

Analog To Digital Converter

The analog to digital converter is a high speed 12-bit converter. It has a front end multiplexer capable of accepting signal from any one of 8 channels. An additional channel (not connected externally) accepts output from an internal solid state temperature sensor. Unfortunately, the present device does not incorporate any programmable gain amplifier, which would have added to its functionality in industrial measurement & control applications.

 

The analog to digital converter has a very flexible mode of operation. Its operation can be controlled by any one of the following:

 

DMA based conversion is a high speed operation. It can perform continuous conversion on the selected channels (in sequential order) and automatically store the conversion results in an external SRAM and all this is carried out without any intervention from microcontroller. The microcontroller can continue to function, while DMA conversion is taking place. Up to 16M Bytes of external SRAM memory can be addressed. It is also possible to set up ADC for performing continuous conversion on a selected channel and store the result in its internal registers. This mode of operation is certainly useful in digital process control.

 

Digital To Analogue Converter

A number of microcontroller have started to boast the on-board presence of high resolution A/D converter (10-12 bit range), but there are not any (are there?) claiming a 12 bit D/A converter, and ADuC812 has not one but two of these channels. The reference voltage is derived from on-board 2.5 volt buried reference common to both A/D and D/A sections. There is a synchronizing bit that can be used to ensure that once input registers are loaded, both the outputs change simultaneously. This is convenient in some applications, such as micro-stepping drives for stepper motors

. 

Flash Program Memory

ADuC812 contains 8K Bytes of flash memory, which can be erased and reprogrammed in one of the following two fashions. The device first needs to be erased before it can be programmed (Perhaps, this requirement will be relaxed in the future versions).


Parallel programming is useful for large production runs. The in-circuit programming (bootstrap loading) is normally designed for programming the microconverter, where the device is already installed in the target application. Because of the flexibility of this mode of programming, this mode can be used for pre-programmed production devices requiring updates or modifications. Any one with a laptop or PC and a terminal software (special) can download a new program into the flash memory of ADuC812.

 

Bootstrap Loading

Bootstrap loading is a very popular feature of Motorola’s HC11 microcontroller family, and it should prove the same for ADuC8XX family of microconverters. This mode is selected by pulling the PSEN pin of microconverter to ground through a small (1 K) external resistor, while the device is under reset. On powering up from reset, a small bootloader code starts to execute. The bootstrap program configures the serial port to operate at 9600 baud at 11.0592 MHz and sends a sign up message. The mating downloader software running on PC can then download the user code in Intel hex format to microconverter.  The downloader software is provided as a part of ADuC812 QuickStart development system. A (www.analog.com) technical note (uC004) is also available from Analog devices with details on serial bootstrap downloading.

 

Data EEPROM

640 Bytes of data EEPROM allow a sizeable amount of user coefficients to be stored in memory including storage of TEDS for multiple transducers. Data EEPROM can be modified through user program. It is not possible to program each byte individually, but only in sectors (groups) of four bytes at a time.  All the bytes in a sector have to erased before these can be programmed.

 

The data EEPROM is not located in 8051 internal register (data) space and can not be directly addressed though user code. Any access to these locations is made through a set of special function registers (SFRs) located in 8051 data space. All read and write (erase/program) operation

make use of these SFRs.

 

Besides the special features highlighted above, ADuC812 still contains the ubiquitous 8051 microcontroller at the core with all its internal and peripheral features. There is a wealth of literature supporting 8051 microcontroller family, which is equally applicable to ADuC812. Anyone familiar with 8051 microcontroller can very quickly develop a measurement and control application, using ADuC812.

 

 

ADuC812 QuickStart Development System

ADuC812 microconverter is amply supported by the QuickStart development system from Analog Devices. It is a relatively low cost system, providing everything a user may need to start experimenting with ADuC812. The development board contains 32K Bytes of SRAM, mapped in external data space and interestingly, an on-board function generator. The function generator can be set to apply triangular, square, or sine wave signals to A/D channel 0 to aid in testing of analogue section.

 

The accompanying CD-ROM contains a full assembler, simulator, and downloading software necessary to transfer the assembled hex files to ADuC. The technical notes related to ADuC found on Analog Devices web site are also included on CD-ROM.

 

Overall, ADuC812 is an excellent device, and improved & more powerful versions are expected to hit the market soon.

 

Acknowledgement:

Author will like to thank Tremont Miao, strategy manager, Analog Devices, for his support in preparing of this article