Vacuum Florescent Display
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[edit] Details
The Vacuum Florescent Display (VFD) became available at Skycraft in Orlando in early July 2009 and was priced at $4.50. The VFD provides a 2 row x 20 character display and accepts ASCII bytes to display characters or perform simple commands. Each character consists of a 5x7 pixel grid.
[edit] Specs
The board is manufactured by NCR (part # CU2000228SCPB-T22C) and was most likely used in cash register machines to display the total price of one's groceries, for example. The display accepts inputs from a 9-pin connector located on the front of the board with Pin 1 marked as the leftmost pin.
| Pin 1 | RS232 RX |
| Pin 2 | RS232 TX (not used) |
| Pin 3 | (not used) |
| Pin 4 | (not used) |
| Pin 5 | +12 VDC (500ma) |
| Pin 6 | +12 VDC (500ma) |
| Pin 7 | GND |
| Pin 8 | GND |
| Pin 9 | Test (hold low on power up) |
The board contains a set of chips that drive the character display.
- 2 Oki C1162A VFD Driver Chips
- 1 DS14C232 EIA-232 Dual Driver/Receiver
- 1 M38002M4 8-bit Microcontroller
The Oki C1162A chips are controlled by the Mitsubishi M38002M4 microcontroller and are responsible for drawing pixels on the VFD. The M38002M4 accepts ASCII commands on it's 1 UART RX line (pin 15) and decodes the input to drive the display. The inputs are simple 8-bit ASCII values received from a host serial device connected to the board's Pin 1 input connector. The RS232 RX line on Pin 1 accepts PC RS232 voltage levels (typically between +/- 12 VDC). The signal is level converted by the DS14C232 so that the microcontroller accepts RS232 signals at the expected 0-5 voltage level.
[edit] How to use
Pins 7 and 8 are tied to the common ground line of the transmitting device (i.e. Pin 5 of a 9-pin Dsub RS232 connector). The board is source by 12VDC at 500ma. This may be aquired from a standard wall wort. Pins 5 and 6 are tied to the 12VDC power input. Pin 1 is tied to the TX line of the external device. The VFD accepts data on this line at 19200 baud, 8 data bits, no parity, and 1 stop bit. The following figure outlines the connection points between the board's input connector and a 9-pin serial connector.
Input ASCII bytes will either show a character on the display at the current cursor position or perform a specific function. Every ASCII character sent by the external device results in an immediate action on the display by the VFD board. The following table details the inputs and their functions (values not listed either have no function or are undefined).
| ASCII Value | Function |
| 8 | Move Cursor Left (backspace) |
| 9 | Move Cursor Right (tab) |
| 10 | Move Cursor Down (linefeed) |
| 12 | Move Cursor To Top Left (formfeed) |
| 13 | Move Cursor To Line Start (carriage return) |
| 14 | Clear Display |
| 17 | Disable Scroll (default) |
| 18 | Enable Scroll |
| 20 | Cursor Off (default) |
| 21 | Cursor On |
| 22 | Cursor Off |
| 23 | Cursor Off |
| 25 | Enable Character Set 2 |
| 26 | Enable Character Set 1 (default) |
| 27 - 255 | Display Visible ASCII Characters |
The ASCII characters displayed for values 27 thru 255 consist of standard alpha-numeric symbols as well as extended symbols similar to ASCII characters used by old IBM PC systems. When a character is displayed the cursor position is updated on space to the right. The cursor is made visible by sending decimal '21'. When visible, the current position is highlighted with a blinking square. The cursor's position may be altered without character display by using commands 8, 9, 10, 12, or 13. Scrolling is enabled or disabled with decimal '17' and '18'. When scrolling is off, the cursor position will wrap around to the top-left position when a character is displayed in the bottom-right position. With scrolling enabled, the VFD will shift the bottom row up and start the cursor on the start of the second row.
