NEC uPD274C in Prinztronic Asset
The uPD274C is a single chip calculator solution manufactured by the NEC Corporation. It can drive the VFD segments directly without the need for additional interfacing circuitry. This IC has two main ports, and one port drives the display, whilst the other port scans the keyboard and the display.
Pinout Voltages
If you have a vintage computer or calculator with this microprocessor IC, then this is very useful information for fault diagnosis. Here is a baseline set of voltages on a working chip. These voltages are present when the calculator is displaying a '0'.
| Pin | Voltage** (V) | VFD TUBE | KEYBOARD |
| 1 | +1.016 | ||
| 2 | -20.10 | Display | |
| 3 | -20.10 | Display | |
| 4 | -20.10 | Display | |
| 5 | -20.10 | Display | |
| 6 | -20.10 | Display | |
| 7 | -20.10 | Display | |
| 8 | -22.46 | Display | |
| 9 | 0 | Not connected | |
| 10 | -20.10 | Display | |
| 11 | -1.30 | ||
| 12 | -6.9 | ||
| 13 | -5.9 | ||
| 14 | +5.3 In | ||
| 15 | +3.7 | ||
| 16 | -6.9 | SCAN | |
| 17 | -1.3 | SCAN | |
| 18 | -20.10 | Display | SCAN |
| 19 | +2.2 | SCAN | |
| 20 | -20.10 | Display | SCAN |
| 21 | -20.10 | Display | SCAN |
| 22 | -20.10 | Display | SCAN |
| 23 | -20.10 | Display | SCAN |
| 24 | -20.10 | Display | SCAN |
| 25 | -20.10 | Display | SCAN |
| 26 | -20.10 | Display | SCAN |
| 27 | -20.10 | Display | SCAN |
| 28 | -0.13 | SCAN |
** All the voltages are with respect to the battery negative.
This Article Continues...
Prinztronic AssetPrinztronic Asset inside Look
Prinztronic Asset Keyboard Assembly
Prinztronic Asset VFD Display Technology
Mannics DC25 Power Module
NEC uPD274C in Prinztronic Asset
Prinztronic Asset Power Supply
Prinztronic Asset Cover
Prinztronic Asset Aesthetics