【正文】 xis. The value of every one of the 10 grids in the Yaxis is equal to the value of related amplitude knob control. With the property node of the waveform graph, you can set the minimum value of each Yaxis as 5 times much as the knob value whereas the maximum value set 5 times. So when you change the amplitude knob value, the minimum and the maximum value of the relevant Yaxis should be changed at the same time, the waveform display can be zoomed as required, and the zero point position is kept in the original location. Use an array to save the amplitude values every Yaxis changed. When a channel is selected, put its old amplitude value to the knob first。 and after adjusting, replace the related array element with the new value. And then the amplitude value change function is finished. C. Time Base Adjustment Time base adjusting is one of the basic functions in oscillograph. The time base adjusting knob39。s value shows the time of every one grid of Xaxis in the screen which is the nodus during the oscillograph design procedure. 1) Basic Clew According to the characteristics of the Graph control, it displays all the data input at a time. So distribute the X axis into 10 grids and make every grid39。s time t. If the waveform could bestride the whole Xaxis, the time spent to collect all the data is 10t. Suppose the board39。s sampling rate is f, in other word, the board collects f data every second. So the number N needed in the waveform is: N= fl0t =l0ft （ 1） Keeping the board sampling at the frequency of f, the program reads N data points from the board memory and put them to the oscillograph in every loop. Change the t value is to change the N value read from board memory every time, and thus adjust the time base in the realtime sampling. But through the experiment we can see, when the time base is too long (100ms) or too short ( 500us), the waveform displayed has time lags to different extend. That is because when the time base is too long (if the length of the needed waveform exceeds 1 second), we must wait for enough time to get all needed data collected by the board, and display them on the screen at a time. So that can cause discontinuous waveform displayed in the screen. When the time base is too short, the N value read every loop is too small, the number of data points in one second should be read for many times. There is another work to be done at the same time every loop in addition. So it will cause that the old data can not be read in time and may be covered by the new data because the board is sampling all time, the board memory will overflow. So it is needed to dispose the number read from board at long and short time base separately. 2) Long time base To avoid the time lag discussed above, it must reduce the number of data read from sampling board every loop. Considering the display characteristics of Graph control, it can not put the data points read from boards to the graph every loop because it will make the oscillograph refreshing all the time, and the waveform displayed could not bestride the whole Xaxis. An array could be set to save the waveform data points displayed. The array39。s capacity is N, which is the number of data points calculated via Eq. (1). 附 錄 4 Suppose the number of data points read from board card every time is a fixed value m, which is the number of data points to be read at the proper time base. The whole procedure is made up of two parts. First, set the whole array NULL. At the beginning of the display procedure, the array is not full. So put the new m data points into the end of the array (Enqueue), and then display the whole array value in the graph control. A continuously moving waveform should be showed in the screen. Second, when the array is full, get rid of first m elements of the array。 move the rest Nm elements forward the beginning of the array。 and put the new m data points into the end of the array. We call this process FIFO. Then a full waveform should be showed in the screen, from one side to the other side. The Enqueue and FIFO are shown in Fig 3. Because the number of data points m read from board card every time is suitable, the time lag caused by waiting for enough data is properly solved. It ensures the synchronization between sample and display. To reduce the time spent to calculate the FIFO procedure by system, sampling frequency should be reduced at the long time base to reduce the capacity of the display array. 3) Short time base In this part, the problem to be solved is that the time lag and memory overflow because the number N calculated via Eq. (1) is too small. The number N could not increase blindly because that will cause the disaccord between the set time base and the waveform displayed. So, a method called EM (expandmove) is put forward. Fix the number to be read in every loop, which usually should be the one at proper time base. Suppose it as m, and the needed number at the short time base calculated via Eq.(1) as N ( N m ). Expand the △ t value of the waveform data by m/N times (expand). At the same time, change the maximum and minimum value of the Xaxis, display the m data points ( △ t expanded) several times in turn, then get into next loop. Until now, the whole procedure is finished. The diagram is shown in and . 附 錄 5 D. Position Adjustment and zero mark Changing the Y value of the waveform data can change the waveform39。s position displayed on the screen. Increasing or decreasing the Y value of the waveform data can move the waveform up or down. To mark every waveform39。s zero position, add a button control to each waveform displayed. Drag the control into a line to mark the zero position. Initialize the control, relative to the oscillograph panel, to the middle of the right screen edge. When changing the position of the wa