Light emitting diode (LED) in such areas as industrial controllers and meters, medical devices and home appliances have a wide range of applications. Traditional LED display driver with 74HC573 and 74LS47 logic device, use the device more, consume more microprocessors I/O port and a larger Board area, especially LED a large number of cases, these shortcomings Nikon Coolpix S8100 Battery Chargerare particularly prominent. In order to overcome these shortcomings, LED display serial interface drives came into being, MAX6950/MAX6951 belonging to the class of the Maxim company introduced drive, less its input pin, driving ability, and the decoder is integrated and brightness controller.

2 MAX6950/MAX6951

MAX6950/MAX6951 is a compact, common cathode display drive, available through SPI, QSPI and MICROWIRE-compatible serial interfaces the microprocessor to the independent or discrete 7 segment LED digital tube, bar LED. MAX6950 can drive or 5-digit 7-segment digital tube LED 40 separation. MAX6951 can drive 8-bits or 64 discrete LED digital tube.

The drive contains 16 hexadecimal characters decoders (0-9,A-F), multiplex scan circuitry, and digital drives and static RAM used to store each number. LED current set by internal digital brightness control circuit.

In addition to data register, there are decoding mode register (16 hexadecimal characters decoder), brightness control register, scan limit register (allows the user to select from 1 to 8-bit display number), the configuration register (clear, flicker, shutdown). Working modes: normal mode and low-power shutdown mode, and forced all the LED turn on test mode.

Because of its unique multiplex scan circuitry, so MAX6950/MAX6951 the small 16-pin QSOP package.

2.1 internal structure

Internal structure as shown in Figure l of MAX6950/MAX6951.

2.1 pin functions

Figure 2 shows the MAX6950/MAX6951 pin QSOP package arrangement, pin functions are described as follows:

DIN (pin 1): serial data input, the CLK and the rising edge data into internal 16-bit shift register.

CLK (pin 2): serial clock input, selected CS force, rising edge of the CLK, data into the internal shift register, at the falling edge of the CLK, DOUT end of data moved.

DIGX/SEGX (PIN 3~6,10~14): drive x inhalation from display altogether cathode current output, x-drive monitor output current,/drive is in a high-impedance state at shutdown time.

ISET (PIN 7): the current set, the resistance between pin and GND RSET, set peak current, the resistors and capacitors with CSET also set multiplexed display of clock frequencies.

GND (PIN 8): power supply.

OSC (PIN 9): multiplexed display clock output.

CS (pin 15): circuit selection inputs, low level, serial data into the shift registers, CS upward along the latch of the last 16-bit data.

V+ (pin 16): Power port.

2.2-how it works

Micro-controller to send 16-bit serial data into the shift registers (sequence as shown in Figure 3), the CS signal to jump into a high level, data is loaded into the 16-bit latch, then on the latch in the 16-bit data to decode and execute the appropriate command. High 8-bit to 16-bit data is address low value is 8-bit registers. About specific sets of registers and control features, see [1].

3 application examples

Following to this circuit is MAX6951 drive the digital display for example. Driven by an industrial controller with MAX695l 8 digital, microprocessor is the ARM7TDMI core LPC2214 PHILIPS company, software development platform for ADS1.2, by programming the MAX6951 control. In this design, did not use the SPI port, but using LPC2214 3 General purpose I/O port (P1.15, P1.16, P1.17). Simulation of Figure 3 sequential transfer data to MAX6951, to complete a variety of control and display functions.

3.1 hardware circuit

Hardware circuit as shown in Figure 4, which DIN, CS and CLK LPC2214 respectively connected to the P1.15, P1.16, P1.17. Because of its unique pin multiplexing requires 8 display (digital) of each line ofPanasonic DMC-TZ1 Battery Charger code is not the same, and each show altogether cathode connections are not the same, as shown in table 1.

3.2 software design

Software includes 3 I/0 initialization, timing and analog inputs to initialize registers to match demand. Control brightness, flashes, and refreshed a number or character display and other functions can be completed by calling the data entry functions, these functions can also be packaged for the child functions to simplify application.

3.2.1 initialize I/O port

Initializes the I/0 macro definition and program code are as follows:

3.2.2 input timing simulation

In accordance with the sequential write input function, as shown in Figure 3, the code is as follows:


3.2.3 circuits initialization

MAX6951 the electricity on, the circuit is in shutdown mode, register with the initial value, for which initialization is needed to meet the system requirements. For instance, initialized to the normal mode, 8 digital tube display "0" brightness to maximum and not blinking, codes are as follows (command words meaning see [1]):

4 similar circuits

Serial LED display of input drive there are many kinds, such as ALLEGRO Corporation A6275/A6276/A6277, STMicroelectronics company (ST) M5450/M5451 series, United States national (NS) LP3943/LP3944 of Texas instruments (TI) TLC59xx series. The less number of drives or drive LED, A6275 (8) and LP3943 (16), or pin a large number, such as the M5451 (PLCC44 or PDIP40), TLC5920 (SSOl48). Also, with built-in decoders and brightness adjustment, and more rarely. MAX6950/MAX6951 deficiency is higher prices and,JVC GR-D796 Battery Chargertherefore, this drive suitable for high requirements such as size, power consumption, and is sensitive to costs are not small or handheld devices.

MAX6950/MAX6951 LED shows the drive easy to use, can do more complex display features, saving board space, set-top boxes, white goods, industrial controllers, medical equipment and instrument, dot-matrix displays, and widely in areas such as the bar.