Wpływ niskich temperatur na szeregową asynchroniczną transmisję danych w systemach pomiarowych z mikrokontrolerem ATmega16A

摘要

w pracy opisano problem cieplnych zmian szybkości asynchronicznej transmisji szeregowej, prowadzonej między blokami systemu pomiarowego. Omówiono komunikację kontrolera systemu z układem ATmegal6A w bloku akwizycji danych. Zaprezentowano wyniki badań oscylatora RC mikrokontrolera ATmegal6A dla temperatur zmniejszanych do 77K. Obliczono błędy szybkości transmisji asynchronicznej na poziomie TTL w systemach pomiarowych z układem ATmega16A, pracujących w zakresie niskich temperatur.%The paper presents a problem of the asynchronous serial transmission between the blocks of a measurement system that works in different temperature ranges. In such conditions the receiver operational range is dependent on the mismatch between the received bit rale and the internally generated baud rate. There is discussed communication of a system controller with an ATmegal6A device within the data acquisition path. In the paper the results of clock signal frequency tests conducted for a calibrated internal RC oscillator of the ATmegal6A microcontroller at low temperatures with the lowest point at 77K, are also presented. There arc shown the low-tempcrahire characteristics of changes of the oscillator frequency for the rated initial values of 1MHz and 8MHz. There are also considered the conditions of effective asynchronous data transmission when a USART module of the ATmegal6A microcontroller is used, because the accuracy of the USART internal baud rate clock depends on the temperature drift of the internal RC oscillator and the length of USART baud rate registers. There are calculated the baud rate error characteristics and the achieved results arc compared with the total error and the recommended receiver error defined for the ATmcga16A USART module. The author formulates conclusions concerning the clocking and the TTL asynchronous operational range of the ATmegal6A microcontroller USART module of measurement systems working at low temperatures.