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SELECTING
A VFD |
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| 1 | Selecting a Module |
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| 2 | Module Construction | |
| 3 | Power Supply Requirements | |
| 4 | Communication Interfaces | |
| 5 | Module Reset | |
| 6 | Software Commands | |
| 7 | Character Sets | |
| 8 | Design Precautions | |
| 9 | Trouble Shooting | |
| Service & Warranty | ||
| Custom Design Modules | ||
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| 1 Selecting a Module | View Module Function Comparison Table | ||||||||||||||
| A VFD module offers
a fast and affordable development path and production solution for
projects both large and small. 20 years experience and continuous research
into new techniques allow us to provide you with a product which has been
designed and manufactured to meet the ever demanding performance of
today's applications. Please determine the factors required for your application prior to making your selection. Cost critical applications may benefit from customizing a high volume standard solution. Please inquire. Although many modules are now available with a combination of interfaces, additional interface modules are available in the MCB range to meet other requirements. The vivid illumination of a VFD means that you can use a smaller character height compared to other technologies. Please view the table for an indication of viewing distance vs. height. We will now review the other factors shown in the table. |
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| 2 Module Construction | |||||||||||||||
| A VFD module typically includes a VFD glass, driver ICs, CPU or ASIC controller, a DC/DC converter and interface connection mounted on a printed circuit board (PCB). Mounting holes are provided at the four corners of the PCB with sufficient clearance for a spacing pillar. The VFD glass is secured to the PCB with pin connections soldered to the PCB. The VFD glass typically has an evacuation pipe extending 6 to 8 mm from the side, but normally this remains within the bounds of the PCB. Although most of the components are surface mouted with a profile less than 2mm, transformers, electrolytic capacitors and connectors will extend 5 to 10 mm from the PCB. Transformer-less modules have been designed to meet the requirement for low profile compact applications. Many modules are designed for IDC connection which are either supplied fitted or allow the user to specify their requirement. |
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| 3 Power Supply Requirements | |
| Most modules operate from a
single 5VDC supply. The exceptions are for specific applications in point
of sale and amusement equipment where 12VDC is the typical supply voltage.
Custom modules have been designed with wide operating capability of 10 to
36VDC for transportation applications. It is important that the power source has a fast rise time and can supply the in rush current where a transformer is used in the DC/DC converter. This can be twice the nominal operating current. Recent designs use a power supply control IC with fixed frequency and soft start. Transformer-less modules have the advantage of being able to start irrespective of how slow the rise time. Particular care should be taken when the module has a separate supply from the host due current flow in the signal/data lines causing incorrect initialisation. |
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| 4 Communication Interfaces | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The following table lists many
popular interfaces used by host systems with their key attributes. A common 0V ground connection is required between host and module except for USB and RS485. |
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| 4.1 Synchronous Serial Interfaces | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| A clock signal output by the
host system provides a synchronizing reference for communicating data bits
on a separate data input/output. The data should be stable on either
rising edge or falling edge of the clock waveform depending on the system
protocol. Since synchronous communication can easily be corrupted by
noise, a reset signal is used prior to critical events to ensure both host
and module are co-ordinated.
A 'clock serial' interface is the simplest
method with single direction 'send' data to module. An additional signal
line C/D may be used for command and data register selection.
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| 4.2 Asynchronous Serial Interfaces | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Communication is achieved by
initiating a change of state in the data signal (start bit) followed by 8
fixed frequency periods (baud rate) for the synchronized transmission of
data. This enables a 2 wire solution for many applications with inherent
re-synchronization after each 8 bit data byte. Transmission between host and module can be made at CMOS/TTL logic voltage levels over distances up to 0.5 metre. The idle state is logic high with data rates upto 115K bits per second. Greater distance is achieved using RS232 voltage levels (+/-12volts) or a differential system like RS485 which uses two signal wires where the logic level is dependent on the polarity of the wires. After each data byte, a period is required to allow the module time to process the received data. A hardware control line can be used to indicate to the host that the module is busy. In certain modules an XOFF (13H) character is transmitted to the host to indicate the receive buffer is full. When ready, the module sends the character XON (11H). |
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| 4.3 Parallel Interfaces | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The conventional CPU distributed
data method uses a parallel 8 bit data bus. Two bus configurations evolved
to provide data transfer control which are known as M68 bus and i80
bus. The M68 bus has an (E)nable clock signal and a direction control signal (R/W). The i80 bus has a separate (/WR) signal for controlling the sending of data and (/RD) for receiving data. Many modules allow either data bus to be connected by configuring a jumper link on the module PCB. Additionally, one of the CPU address lines
(A0 through to A15) can be used to select different data registers inside
the module via the Rs, C/D or A0 input. This allows many additional
display functions to be performed with a single command byte. |
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| 4.4 Other Interfaces | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Wireless, Ethernet and Optical interfaces have evolved for messaging applications. Interface modules are available in the market to convert these interfaces to RS232. |
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5 Module Reset Power On Reset |
| When power is applied to the display module, an internal reset circuit ensures the internal micro-controller or ASIC initializes correctly. The host system should allow at least 100ms before sending data to the module. |
| Hardware Reset |
| Modules with a hardware reset allow the host system to restart the initialization sequence to ensure system integrity. The specification will define the period which should be allowed before data is transmitted. |
| 6 Software Commands | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The extent of the software commands in a
module will determine it's flexibility to show data efficiently. Cost constraints can restrict the commands available. |
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| 6.1 Character Display Commands | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| T Series - Standard ASCII | U Series - LCD Compatible | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| 6.2 Graphic Display Commands | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
GU-K6xxx4 Series
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GU-3000 Series
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