Philips pm2521 - Page 31

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4.2. CONTROL SECTION
The heart of the control section of the PM 2521 is a 8035 microcomputer.
A 4k ROM is used as program memory. In the control section the data acquisition takes place.
Inputs for the control section are : the mode switches
the function selector
the counter output
» the ROM
Outputs for the control section are : the display
. the relay control
In general the following actions are made by the microcomputer /ROM.
INPUT/OUTPUT ACTIONS
MODE SWITCHES
Range commands
4
In autoranging mode:
Check if the counter output is higher or lower than a certain value.
If so, select a higher of lower range. Display of the decimal point.
In manual ranging mode:
Select a higher or lower range on up or down commands of the UP
or DOWN pushbuttons. Display of the decimal point.
STOP/RESET commands
Stop the time measurement.
Reset the time measurement.
+/— commands Set the + or — trigger level.
dB (V—-) command Set the dB function and convert the ac voltage into a dB value.
ZERO SET command
Set the relative reference value and display each subsequent positive
*
or negative deviation of the relative reference value.
FUNCTION SELECTOR
Set the direction of the input signal in the analog section.
Display the function indication.
THE COUNTER OUTPUT Display the counted data including the polarity.
If the counter output exceeds the end of range value, display OL.
THE DISPLAY
Display the counter data, the decimal point and the function
indication.
THE RELAY CONTROL
Supply the range and function information to the analog section,
where the attenuation factors, the sensitivity of the ADC and RMS
convertor, and the direction of the input signal are set.
4.3. DISPLAY SECTION
The display section consists of a liquid crystal display interface and the liquid crystal display (LCD).
The display section is directly controlled by the microcomputer. The data from the microcomputer is
supplied to the LCD interface in serial form.