| PIN DESC | RIPTION | | |
| Pin No. | Pin No. | | |
| (40-Pin | (44-Pin Flat |
| Package) | Package) | Symbol | Description |
| 20 | 16 | DPO/LO | Dual-purpose input. Decimal point select input for voltage measurements. In logic mode, connecting this pin to VDD will turn on the "low" LCD segment. There is an internal 5ccA pull-down to DGND in volts mode only. Decimal point logic: DPl DPO Decimal Point Selected |
| 0 0 None 0 1 DP1 1 0 DP2 1 1 DP3 |
| 21 | 17 | DPl/HI | Dual-purpose input. Decimal point select input for voltage measurements. In logic mode, connecting this pin to VDD will turn on the "high" LCD segment. There is an internal 5ccA pull-down to DGND in volts mode only. |
| 22 | 18 | BUZOUT | Buzzer output. Audio frequency, 5kHz, output which drives a piezoelectric buzzer. |
| 23 | 19 | BUZIN | Buzzer control input. Connecting BUZIN to VDD turns the buzzer on. BUZIN is logically ORed (internally) with the "logic level low" input. There is an internal 5ccA pull-down to DGND. |
| 24 | 20 | FREQ/ | Voltage or frequency measurement select input. When unconnected, or connected |
| VOLTS | to DGND, the A/D converter function is active. When connected to VDD, the frequency counter function is active. This pin has an internal 5ccA pull-down to DGND. |
| 25 | 21 | PKHOLD | Peak hold input. When connected to VDD, the converter will only update the display if a new conversion value is greater than the preceding value. Thus, the peak reading will be stored and held indefinitely. When unconnected, or connected to DGND, the converter will operate normally. This pin has an internal 5ccA pull-down to DGND. |
| | 22 | UR | Underrange output. This output will be HIGH when the digital reading is 380 counts or less. |
| | 23 | OR | Overrange output. This output will be HIGH when the analog signal input is greater than full scale. The LCD will display "OL" when the input is overranged. |
| 26 | 24 | VSs | Negative supply connection. Connect to negative terminal of 9V battery. |
| 27 | 25 | COM | Analog circuit ground reference point. Nominally 3.3V below VDD. |
| 28 | 26 | CREF | Positive connection for reference capacitor. |
| 29 | 27 | CREF | Negative connection for reference capacitor. |
| 30 | 28 | VREF | High differential reference input connection. |
| 31 | 29 | VREF | Low differential reference input connection. |
| 32 | 30 | VIN | Low analog input signal connection. |
| 33 | 31 | vTN | High analog input signal connection. |
| 34 | 32 | VBUFF | Buffer output. Connect to integration resistor. |
| 35 | 33 | CAZ | Auto-zero capacitor connection. |
| 36 | 34 | VINT | Integrator output. Connect to integration capacitor. |
| | 35 | EOC/ | Bidirectional pin. Pulses low (i.e., from VDD to DGND) at the end of each |
| HOLD | conversion. If connected to VDD, conversions will continue, but the display is not updated. |
| 37 | 36 | OSC1 | Crystal oscillator (input) connection. |
| 38 | 37 | OSC2 | Crystal oscillator (output) connection. |
| 39 | 38 | OSC3 | RC oscillator connection. |
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