To customize the four 7-segment LED display driver chip, for example, the design of the LED display to drive the principle shown in Figure 7. It uses the 89C52 microcontroller’s general-purpose I / O port the P1.0, P1.1, as a simulation of the I2C bus; LED display for four common cathode LED pin is connected to the power of the A / K; display driver chip P87LPC762 for custom, named for the LED lights -762. I2C bus external address of the first chip 000, A0, A1, A2 pin to ground to achieve the rest of the chip address set in turn, can connect up to 8 external chip (not shown). From the schematic point of view, LED-762 can not add any external components can be used as LED drivers, I2C bus connections, take up system resources, at least, the circuit is relatively simple. Connected on the I2C bus, eight LED-762 LED extended median of 32. LED display driver chip applications, can use the same connection for the “m” field. The “m” field LED on the same I2C bus, the maximum extension of 48, enough to meet the general requirements.
In order to improve the driving capability of the I2C bus, in the realization of multi-chip connections, SCL, the SDA should be connected bus matching pull-up resistor.
Software programming of customized LED panel display driver chip
Was controller within the LPC series chips with hardware support for I2C bus interface, the user can direct it as the master of the I2C bus or the I2C bus. Controller via the I2C hardware interrupt handler can receive or send data from the bus; master operation, the I2C bus to the start timing, data timing, response timing, stop timing to detect the I2C bus controller, and corresponding data transfer. On the I2C bus controller based on the I2C bus address to distinguish. The unity of the I2C bus addresses allocated by the I2C bus Commission, a total of seven chip address (it occupies D7 ~ D1-bit), 4 (D7 ~ D4) decided to chip types, users can also customize the chip types, 3 (low D3 ~ D1) chip A0, A1, A2 pin set.
When used with the LPC series of I2C bus interface chip custom LED display driver chip, customized LED display driver chip is set to be the controller, you want to send data the CPU is set to the I2C bus master. Customized LED display driver chip to receive data through the I2C interrupt the flow chart shown in Figure 8. When the first data received from the I2C bus, the judgment of the chip address, such as the same and write to display data, then send the response timing receiver 4 displays the data, then the I2C interface to return to the idle state. LED dynamic display, LED display drive-based display program according to the LED polarity input, respectively, sent to display segments and bits, and the LED tube will be able to display properly.
According to the I2C bus protocol requirements, response time requirements for the master to send data. The shortest period of time determined by the multiplier of the RC oscillator frequency and interrupt response time to the maximum rate can reach 400kbs / s. The minimum rate may be within the LPC series dedicated I2C timer to control, in order to adapt to the low rate of non-standard I2C bus operation, off timer.
6-chip testing and key performance indicators
Requirements in accordance with custom, the complete LED curing of the driver and chip set the parameters by the programmer to the production of chip testing the connection diagram shown in Figure 7. The 89C52 P1.0 and P1.1 as analog I2C bus control line, write simulation I2C driver. A normal data reception, 89C52 host re-reset the I2C bus communication disconnection, and other circumstances can not affect the display driver. If you turn off the timer in custom LED driver I analog I2C program pause, single step debugging custom LED driver can drive display. By Philips LPC series chip port output current capability, 0.5 in. drive common cathode and common anode LEDs, LED brightness are to meet the requirements. In the long-term full-bright display, custom LED driver chip temperature normal, long-term continuous work. In actual use, control, Port A / K and A0, A1, A2 set the input mode when the programming, so the vacant when the input level is undefined, and random variation, and may not display properly, should be based on the address set requirements that force is connected to VCC or GND.