Interface and Application of BC7281B and DSP

In DSP application systems, commonly used input and output devices are LED digital tubes and keyboards. The original data information is input through the keyboard, and the processing results of the single-chip microcomputer are output by the digital tube. When a large number of external keyboards and digital tubes are relative to the limited single-chip microcomputer port resources, a dedicated interface chip is needed to expand, and BC7281 meets this requirement. It can control up to 16 digital tubes or 128 independent LED tubes.

1 Introduction to BC7281B
BC7281 chip is a new type of 16-bit LED digital tube display and keyboard interface dedicated control chip. The chip uses a high-speed two-wire interface to communicate with the MCU, occupying only a small amount of I/O port resources and host time. The BC7281 chip can connect to a keyboard matrix with up to 64 keys, and has an internal de-jitter function. BC7281B also adds a "register protection" (anti-interference) mode to further improve the anti-interference ability.
1.1 BC7281B pin description
This system uses the BC7281B chip, and the pin description is as follows:

1.2 BC7281 byte write and read timing
The BC7281 byte write and read timing is shown in Figure 1.

2 Introduction to TMS320F812 DSP
The TMS320F2812 chip is a new member of TI's DSP controller 2000 series. TMS320F2812 provides powerful computing power, with a maximum operating speed of 150MIPS. It has the characteristics of strong processing performance, high peripheral integration, large program memory and fast A/D conversion speed. It is widely used in the fields of digital control of motors. TMS320F2812 adopts high-performance static CMOS technology, with a power supply voltage of 3.3 V, and has a variety of low-power working modes, which can fully reduce system power consumption.

3 Hardware interface and software design of BC7281B and DSP TMS320F2812
The control chip used in this system design is BC7281B, and the DSP chip is TMS320F2812. During the design process, a 20k pull-up resistor is connected to the DAT line to enable it to reliably output a high level. The DAT and CLK signal lines connected to the DSP are connected in a twisted pair with the ground line, and a filter capacitor is connected between each signal and the ground to improve the anti-interference ability. In order to better improve the anti-interference ability of the BC7281B power input terminal, an RC filter circuit is connected in series between the VCC power pin and the power supply to filter out the spikes and glitches in the power supply. The external RC oscillation circuit of the BC7281B uses a 1.5k resistor and a 20pF capacitor to provide a 9.5MHz clock. For the bit drive circuit, this design uses a common anode digital tube, the triode is connected in an emitter follower form, and a 100k current limiting resistor is added to the base.
3.1 Hardware interface circuit of BC7281B and DSP TMS320F2812
The specific interface circuit of BC7281 B and DSP TMS320F2812 is shown in Figure 2.

As shown in Figure 2, DSP transmits data with the data transmission line DAT and synchronous clock line CLK of BC7281B through the I/O interface (IOF10 and IOF13). The CLK pin is controlled by DSP and the falling edge is effective. R/W in the instruction byte is read-write control. When R/W=0, DSP writes data to the internal register of BC7812B; when R/W=1, DSP reads the data of the internal register of BC7812.

3.2 Software Design
The software flow chart is shown in Figure 3:

The specific procedures are as follows:

4 Conclusion
BC7281B effectively solves the problem of hardware cost and MCU IO port resource occupation in DSP application system. The chip is easy to use, stable and reliable, and flexible to program. In engineering applications, it is the best choice for designers. I have successfully used this chip in many products, and achieved twice the result with half the effort.