Realize multiplexing or compression of hardware resources by serial communication

"Serial port download" is the program that most engineers first contacted, especially the engineers who started using 51 MCUs. As hardware integration becomes higher and higher, and chip resources are continuously compressed, engineers also think of another "serial download" method, which requires only one data line.

With the rapid development of the semiconductor industry, the chip integration is getting higher and higher, and the PCBA size that has been developed and designed has been able to compete with coins, but the function has not been affected at all. How is it done? It is a headache for every engineer to cut hardware resources without affecting the function. The key is how to ensure that the programming can be carried out normally after cutting.

There are a variety of programming interfaces, including UART, I2C, SPI, SWD, etc., which are familiar to engineers. Generally, 2-6 lines are required for programming, and one of the programming interfaces requires only one data line to program the program. This is a good news for engineers who must try to compress hardware resources.

Figure 1 Coin-sized PCBA

PCBA, which is the size of a coin, is not uncommon today. To integrate well-functioning functions in such a small volume, hardware resource multiplexing or compression is a reliable means, in which programming operations can be performed using as few interfaces as possible to achieve compression hardware. The purpose of the resource.

Single line serial port

A single-wire serial port is a communication method for a serial interface. Serial interface refers to the sequential transmission of data one by one. It is characterized by simple communication lines. As long as a pair of transmission lines can realize two-way communication (you can directly use the telephone line as a transmission line), the cost is greatly reduced. Especially suitable for long-distance communication, but the transmission speed is slow. The communication method in which the data of one piece of information is transmitted in order by bit is called serial communication. The characteristics of serial communication are: the transmission of data bits, in bit order, at least one transmission line can be completed.

Figure 2 serial data frame

Single-line serial port: Fully referred to as "single-line asynchronous serial communication interface", referred to as "single-line serial port" in this paper.

Standard serial port: Fully referred to as "standard asynchronous serial communication interface", referred to as "standard serial port" in this paper.

The two use the same communication protocol, the difference is that the standard serial port uses two data line communication (TXD and RXD), the single-line serial port has only one data line to have both sending and receiving functions . Therefore, the single-wire serial port adopts half-duplex communication mode. The specific single-line serial port wiring diagram can be referred to the following figure.

Figure 3 Schematic diagram of single-line serial cable

As can be seen from the figure, you only need to access four lines (MOD, /RESET, VCC, GND) to program the program. Only one of them is a data line for sending and receiving data.

The communication port (MOD/IO) marked on the chip can also be used to select the working mode. For example, at the same time of power-on reset, the input timing waveform of the MOD pin is detected, and according to the timing waveform, it is judged to enter different working modes. For example, enter the single-line serial programming mode. After entering the single-line serial programming mode, the function of the MOD pin is converted to data communication. This can minimize the programming port used by the program to achieve further compression of hardware resources. Master this rule, after P800isp connects these four lines, you can easily achieve the burning.