M204SD01B VFD Module
The NCR 7454 / Futaba M204SD01B VFD (vacuum fluorescent display) module is a large, bright, high quality display capable of displaying 4 rows of 20 character wide text. Each character is formed from a 5x7 dot matrix. These displays are made specifically for the NCR 7454 point of sale system, however new, surplus units are available inexpensively and are easily driven by the Arduino with as few as 8 pins. The Ncr4X20Vfd library was created specifically for this display.
The details on this page were arrived at by piecing together information from material linked to at the bottom of this page; examination and measurement of the display board; examination of an NCR 7454 point of sale system and experimentation.
Specifications
| Item | Specification |
|---|---|
| Supply Voltage | 5V |
| Supply Current Typical | 800mA |
| Supply Current Max | 1A |
| Communction Protocol | IEEE 1284 Parallel |
| Connector | Standard 30 Pin IDC |
| Pinout | Proprietary (See Below) |
The datasheet for the similar M204SD01AA display is linked to at the bottom of this page. Electrical and physical characteristics of the M204SD01AA may be the same or similar to this display. The M204SD01AA however has different electronics, connections, software interface, etc.
Caution: While the display operates on 5V, higher voltages are generated on board. As with all VFDs, the display board should not be operated outside of an appropriate enclosure.
Pinout
In the above image of the rear of the board, pin 1 is located at the top right of the IDC connector.
| Display Pin | Arduino Pin |
|---|---|
| 1 | D0 |
| 2 | D1 |
| 3 | D2 |
| 4 | D3 |
| 5 | D4 |
| 6 | D5 |
| 7 | D6 |
| 8 | D7 |
| 9 | /STROBE |
| 10 | GND |
| 11 | S? |
| 12 | GND |
| 13 | BUSY |
| 14 | GND |
| 15 | S? |
| 16 | GND |
| 17 | S? |
| 18 | S? |
| 19 | /RESET |
| 20 | C? |
| 21 | GND |
| 22 | GND |
| 23 | GND |
| 24 | GND |
| 25 | GND |
| 26 | VCC |
| 27 | VCC |
| 28 | VCC |
| 29 | N/C ? |
| 30 | N/C ? |
Power-Up Diagnostics
Upon power-up the display performs a startup sequence consisting of all pixels being lit for approximately 2 seconds, followed by the part and version number (008-0221552 V1.02.00) displayed for two seconds. According to NCR documentation, a RAM self test is performed first and the display will halt operation of any problems are discovered.
During the power-up sequence the BUSY line is held high.
Communication Protocol
The communication protocol is IEEE 1284 parallel port as was commonly used by PC's to communicate with printers. According to NCR documentation the display supports ECP (Enhanced Capability Port) in addition to standard Centronics. Only Centronics mode has been tested.
The following sequence can be used to send a character to the display:
- Drive all control pins high (/STROBE, /RESET, C?s)
- Wait for the BUSY line to go low
- Place the character data bits on D0-D7
- Drive /STROBE low
- Wait 0.5 us
- Drive /STROBE high
Characters are immediately displayed to the current cursor location.
Control Codes
The following are special control characters/character sequences.
- 08h - Backspace. Moves cursor one space leftward
- 09h - Tab. Moves cursor one space rightward
- 0Ah - Line feed. Moves cursor down to the next row
- 0Ch - Home cursor to top left corner
- 0Dh - Carriage return. Moves cursor to leftmost position of current row
- 0Eh - Clear screen and home cursor to top left corner
- 11h - Vertical scroll off *. When the cursor would advance off the bottom of the screen, it wraps to the top of the screen
- 12h - Vertical scroll on. When the cursor would advance off the bottom of the screen, the display contents scroll upward and the cursor remains on the bottom row
- 15h - Turn on blinking cursor
- 16h - Turn off blinking cursor *
- 17h - Turn off blinking cursor *
- 18h - Select international character set *
- 19h - Select Japanese character set
- 1Ah - Select Code Page 850 character set
- 1Bh 04h - Starts diagnostic sequence. After sending this instruction sequence the display will enter a diagnostics mode and stay in that mode until ended. The diagnostic sequence starts by setting all pixels, then displaying the part number and firmware version, followed by stepping through every character in every character set. One character is shown at a time, filling all positions of the display for approximately 1 second per character
- 1Bh 05h - Display on *. If the display is in low power mode, this will restore the display. If the display is in diagnostic mode, diagnostic mode will be entered. In either case, the prior display contents will be restored
- 1Bh 06h - Display off. The display is blanked and enters low power mode
* This is the power on default
Character Sets
International Character Set
Japanese Character Set
Code Page 850 Character Set
Additional Information
- Ncr4X20Vfd library for driving this display
- M204SD01AA datasheet
- NCR 7454 User's Guide contains specifications and details for this display, however most of the command descriptions appear to be incorrect
- NCR 7454 Service Guide
- IEEE 1284 parallel port information
- Forum post discussing this display