Abstract:
The present invention discloses a set of devices in cascade for driving display devices. For each of the driving devices, the serial-data-in pin and the serial-data-out pin traditionally used to transfer image data can further deliver commands from and/or internal statuses of the driving devices to an external controller. Accordingly, inventive functions of command transfer and/or status feedback can be achieved without adding extra pins. The present invention also discloses a device suitable for forming the driving set, in which a command register and/or a status register is provided.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a set of devices, which are particularly suitable for driving display devices. The present invention also relates to a driving device suitable for forming the set. 
   BACKGROUND OF THE INVENTION 
   Traditionally, sets of LED drivers are applied to driving display devices, e.g. LEDs and VFDs (vacuum fluorescent displays). The display devices are usually placed in matrix, manufactured in a plane, to create and present planar visual information, like images, pictures, and videos. The display devices discretely represent the pixels of the visual information and are driven by the driving devices. By changing the image data which will be stored in the image data register for each discrete pixel sent to the driving device, the visual content displayed can be varied as desired. 
   To effectively lower the cost of the driving devices, (for example, to lower the package cost of integrated circuit chips), only limited package pins are applied. Using merely five signal pins and the pins of the exact pin count equal to output port count, the image data are sent to the driving devices which then light the display devices. As shown in  FIG. 5 , no redundant pins are provided. 
   The driving devices generally comprise of a current-setting circuit  916 , N current-output ports  915 , N current-output pins, a serial buffer  911  of N bits, and an image data register  914  of N bits. 
   The serial buffer  911  conventionally works with three signal pins, clock (CLK), serial-data-in (SDI), and serial-data-out (SDO). 
   When more than one device works in cascade, the CLK pin in all devices are commonly controlled by a set of synchronous signal sources. 
   The data in the serial buffer  911  can be transferred to the image data register  914  in parallel, and the transfer is triggered by a signal pin, LE!. 
   When a signal pin, OE!, receives enable signals, the output ports  915  are capable of delivering driving energy (electrical current or voltage), according to the content in the image data register, at least to light the LEDs. 
   The content in the image data register can be a set of zeros or ones. If ones represent that the LEDs will be lit, zeroes represent that the LEDs will not be lit, and vice versa. 
   To improve the accuracy, to give more sophisticated control, and to provide the feedback functions, usually more functional circuitry will be designed and manufactured in the driving devices. However, to exploit these added features, more input pins and output pins will always be required. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a set of devices for driving display devices, which performs traditional functions of lighting the display devices and exhibits inventive features of command transfer and/or status feedback without increasing the number of pins needed on the display drivers. 
   Another object of the present invention is to provide a device for driving display devices, which possesses traditional functions of lighting the display devices in a display mode and exhibits inventive features of command transfer and/or status feedback in a non-display mode without increasing pins. 
   In this specification, the “display mode” indicates a mode in which the function of lighting the display devices is performed, and the “non-display mode” indicates a mode in which a function other than lighting the display devices is performed. Additionally, the pin described in this specification is not restricted to a pin-shaped means, and can be any lead, element or means capable of receiving or transferring information or data or signals. If the content in the image data register are not to light the LEDs, they are called non-image data. Generally, the non-image data may be the control to be sent to the driving device and may be called command data, and the non-image data may be the feedback to be read from the driving device and may be called status data. 
   In order to achieve the above objects, each of the driving devices in the set comprises a clock pin, a serial buffer, a serial-data-in (SDI) pin to receive at least image data and a serial-data-out (SDO) pin to transfer at least image data. The clock pin can receive clock signals and make image and/or command and/or status data to be serially shifted to and out from the serial buffer through the SDI pin and the SDO pin. For all of the driving devices, the clock pins are commonly controlled by a set of synchronous signal sources. The driving devices can be connected in cascade and sequentially defined as driving device  1 , driving device  2 , . . . , driving device P- 1 , and driving device P; wherein P is an integer larger than 1. Additionally, the SDI pin of the driving device  1  further receives command from an external controller, and the SDO pin thereof further transfers command and/or internal status of the driving device  1 . The SDI pin of the driving device  2  further receives command and/or status from the SDO pin of the driving device  1 , and the SDO pin thereof further transfers command and/or internal status of the driving devices  1  and  2 . Analogically, the SDI pin of the driving device P further receives command and/or status from the SDO pin of the driving device P- 1 . 
   In general, when the internal statuses of the driving devices are transferred by SDI pins and SDO pins thereof, status feedback can be further accomplished by connecting the SDO pin of the driving device P with the external controller to form a loop. 
   In the present invention, the device for driving at least one display device can work in the display mode and the non-display mode. In addition to the serial buffer of N bits, the SDI pin, the SDO pin and the clock pin, the driving device primarily includes at least one extended register of K bits, an image data register of N bits, N output ports, an output-setting circuit, N output pins, a first control pin and a second control pin, wherein N is an integer larger than 1, and K is an integer less than or equal to N. 
   The output-setting circuit, for example, the current-setting circuit, and the image data register are connected to the output ports. The extended register, when enabled by a correspondent signal in the non-display mode, can transfer status of the driving device to the serial buffer and/or receive command data from the serial buffer. Each of the output pins, for example, the current-output pins, is connected to a corresponding output port, for example, the current-output ports, so as to drive a corresponding display device. The first control pin, for example, the latch-enable pin, is to trigger the serial buffer to transfer data in parallel to the image data register. The second control pin, for example, the output-enable pin, is to enable the output ports to deliver driving energy, electrical current or voltage, to the output pins. 
   The extended register can be a status register capable of transferring internal status of the driving device to the serial buffer, or a command register capable of receiving command from the serial buffer in the non-display mode. 
   The correspondent signal for enabling the extended register can be sent from a mode-switch circuit, while the mode-switch circuit receives preset signals from the first control pin and the second control pin within a duration. Particularly, the mode-switch circuit can be connected to the clock pin so as to receive the preset signals which are based on a discrete time scheme determined by the clock pin. In order to convert the driving device from the display mode into the non-display mode, the preset signals aforementioned can be a first signal received by the second control pin and a second signal followed by the first signal and received by the first control pin. On the other hand, in order to convert the driving device from the non-display mode into the display mode, the preset signals can be a first signal received by the second control pin and an unchanged second signal continuously received by the first control pin within the duration. 
   Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows the driving set of the preferred embodiment in accordance with the present invention. 
       FIG. 2  shows the internal connection of the driving device in accordance with the present invention. 
       FIG. 3  shows a preset sequence for determining the driving device to enter the non-display mode from the display mode. 
       FIG. 4  shows another preset sequence for determining the driving device to enter the display mode from the non-display mode. 
       FIG. 5  shows the internal connection of the traditional driving device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a driving set  1  of a preferred embodiment in accordance with the present invention. In this embodiment, the driving set  1  is composed of four similar driving devices of eight bits, marked as items  10 ,  20 ,  30  and  40 . The driving devices  10 ,  20 ,  30 ,  40  are connected in cascade to drive a 4×8 LED array. The driving set  1  is connected to an external controller  8  to form a loop, wherein the controller  8  can perform general functions such as coding, etc. 
     FIG. 2  shows an internal structure of the driving device  10 , in which a serial buffer  11  of eight bits, a command register  12  of four bits, a status register  13  of four bits, an image data register  14  of eight bits, eight current-output ports  151 - 158 , a current-setting circuit  16 , a mode-switch circuit  17 , an analog/digital converter  18 , eight current-output pins  191 - 198 , a clock pin CLK- 1 , a serial-data-in pin SDI- 1 , a serial-data-out pin SDO- 1 , a latch-enable pin LE!- 1  and an output-enable pin OE!- 1  are included. For all of the driving devices, the clock pins are commonly controlled by a set of synchronous signal sources. 
   When the driving device  10  works in the display mode, according to the content in the image data register, the output ports  151 - 158  are at least capable of lighting the LEDs respectively through the correspondent output pins. That is, clock signals are sent to the serial buffer  11  through the clock pin CLK- 1  and make image and/or command and/or status data to be serially shifted to and out from the serial buffer  11  through the SDI- 1  pin and the SDO- 1  pin. In display mode, the serial data primarily include only image data. These image data will be transferred in parallel from the serial buffer  11  to the image data register  14  in a moment of a latch-enable signal received by the pin LE!- 1 . These image data will be further transferred from the image data register  14  to the current-output ports  151 - 158 . The pin OE!- 1  enables the current-output ports  151 - 158  to deliver driving current to the correspondent current-output pins  191 - 198  from the current-setting circuit  16 , and then the correspondent LEDs can be lit. 
   The above functions performed in the display mode are also well known for traditional driving devices. However, in the present invention, additional functions, command transfer and status feedback, can be further exhibited in the non-display mode and no additional pin is required. The pins LE!- 1  and OE!- 1  are to determine time for switching the driving device between the display mode and the non-display mode. In this embodiment, a synchronous method is applied, in which the pins LE!- 1 , OE!- 1  and CLK- 1  are individually connected to the mode-switch circuit  17  as shown in FIG.  2 . The pin CLK- 1  provides a time unit T for counting based on a discrete time scheme. 
     FIG. 3  shows a preset sequence for determining the driving device  10  to enter the non-display mode from the display mode. In this sequence, two stages, which occur within a duration T 0 , are considered. 
   1) When a first preset signal with a pulse width T 1  is received by the pin OE!, the driving device  10  enters the first stage. 
   2) After entering the first stage, a second preset signal with a pulse width T 2  received by the pin LE! indicates that the second stage is completed, and the driving device  10  enter the non-display mode from the display mode. 
   When entering the non-display mode, the command register  12 , the status register  13  and the mode-switch circuit  17  are enabled. 
   For one of several possible situations, anyone of LEDs might not be lit, and the mode-switch circuit  17  may send a signal as a trigger to make the status register  13  transfer internal statuses of the driving device  10  to the serial buffer  11 . Such status information will be finally sent to the external controller  8  through the pin SDO- 1  and the driving devices  20 - 40 , whereby an operator may take action if the status information indicates that corrective action is necessary. In this situation, the serial data primarily include the status and image data. 
   As for another possible situation that an LED might be lit, but not as brightly as expected, the external controller  8  may send a command to the serial buffer  11 , and then the mode-switch circuit  17  may send another signal as a trigger to make the serial buffer  11  transfer the command to the command register  12 . In this embodiment, the command, containing a gain value, can be further sent to the current-setting circuit  16  through an analog/digital converter  18 , whereby output of the correspondent current-output ports  151 - 158  can be determined by the gain value. 
     FIG. 4  shows another preset sequence for causing the driving device to enter the display mode from the non-display mode. In this sequence, two stages, which occur within the duration T 0 , are considered. 
   1) When a first preset signal with a pulse width T 1  is received by the pin OE!, the driving device  10  enters the first stage. 
   2) After entering the first stage, an unchanged second preset signal continuously received by the pin LE! within T 0  indicates that the second stage is completed, and the driving device  10  quits the non-display mode and returns to the display mode. 
   In the present invention, the pulse widths T 1  and T 2  are short enough, for example, about 1/30 second, which cannot be perceived by human eyes. Therefore, switching between the display mode and the non-display mode is acceptable. Additionally, since the sequence shown in  FIG. 3  is seldom used to drive the display devices, its impact upon the visual effect can be ignored. 
   The above description illustrates internal connection and operation of the driving device  10 . In common use, driving sets such as that shown in  FIG. 1  are provided. In  FIG. 1 , serial data are sent through the pins SDI- 1  and SDO- 1  of the driving device  10 , the pins SDI- 2  and SDO- 2  of the driving device  20 , . . . , the pins SDI- 4  and SDO- 4  of the driving device  40 , finally to the external controller  8 . 
   The driving device of the present invention can further include a circuit for detecting malfunctions of the current-output ports. The statuses can be transferred to the status register for feedback as described above in the non-display mode. 
   According to the present invention, additional functions, command transfer and status feedback, can be enabled without adding extra signal pins to the driving device. Furthermore, the driving set composed of the driving devices in cascade can be applied to the display devices in practice.