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TC820CPL データシート(PDF) 11 Page - Microchip Technology |
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TC820CPL データシート(HTML) 11 Page - Microchip Technology |
11 / 28 page © 2002 Microchip Technology Inc. DS21476B-page 11 TC820 3.2.7 10:1 RANGE CHANGE The analog input full scale range can be changed with the RANGE/FREQ input. Normally, RANGE/FREQ is held low by an internal pull-down. Connecting this pin to VS+ will increase the full scale voltage by a factor of 10. No external component changes are required. The RANGE/FREQ input operates by changing the integrate period. When RANGE/FREQ is connected to VDD, the signal integration phase of the conversion is reduced by a factor of 10 (i.e., from 2000 counts to 200 counts). For the TC820, the 10:1 range change will result in ±4V full scale. This full scale range will exceed the Common mode range of the input buffer when operating from a 9V battery. If range changing is required for the TC820, a higher supply voltage can be provided, or the input voltage can be divided by 2 externally. 3.3 Frequency Counter In addition to serving as an analog-to-digital converter, the TC820 internal counter can also function as a fre- quency counter (Figure 3-3). In the Counter mode, pulses at the RANGE/FREQ input will be counted and displayed. The frequency counter derives its time-base from the clock oscillator. The counter time-base is: EQUATION 3-5: Thus, the counter will operate with a 1-second time- base when a 40kHz oscillator is used. The frequency counter accuracy is determined by the oscillator accu- racy. For accurate frequency measurements, a crystal oscillator is recommended. The frequency counter will automatically select the proper range. Auto-range operation extends over four decades, from 3.999kHz to 3.999MHz. Decimal points are set automatically in the Frequency mode (Figure 3-4). The logic switching levels of the RANGE/FREQ input are CMOS levels. For best counter operation, an exter- nal buffer is recommended. See the applications sec- tion for details. 3.4 Logic Probe The TC820 can also function as a simple logic probe (Figure 3-5). This mode is selected when the LOGIC input is high. Two dual purpose pins, which normally control the decimal points, are used as logic inputs. Connecting either input to a logic high level will turn on the corresponding LCD annunciator. When the "low" annunciator is on, the buzzer will be on. As with the fre- quency counter input, external level shifters/buffers are recommended for the logic probe inputs. FIGURE 3-3: TC820 COUNTER OPERATION tCOUNT = FOSC 40,000 Data Latch, Peak Hold Register, LCD Decoder/Drivers Over Range Detect Under Range Control Auto-Range Control Programmable Divider ( ÷1, 10, 100, 1000) Clock Oscillator To Decimal Point Drivers Frequency Input RANGE/ FREQ ÷20,000 From Integrator of A/D Converter Comparator LCD 3-3/4 Digit Counter Enable Count Overflow A/D Converter Frequency Counter A/D Converter/Frequency Counter Select TC820 ÷2 FREQ/ VOLTS |
同様の部品番号 - TC820CPL |
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同様の説明 - TC820CPL |
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