Shulou(Shulou.com)06/01 Report--

With the development of skills, there is a small amount of use of RS232 serial communication in industry, but in the use of trade skills, we have gradually used USB to UART instead of RS232 serial port. Most notebook computers have no serial port, so what should we do to complete the communication between single-chip microcomputer and computer?

We only need to add a USB to serial port chip in the circuit to successfully complete the conversion between the USB communication protocol and the standard UART serial communication protocol. On our development board, we use the chip CH340T, as shown in figure 11-5.

Figure 11-5 USB to serial port circuit

J1 and J2 at the bottom left of the picture are a combination of two jumpers. Everyone can find them on the lower left of our board. We need to use a jumper cap to short connect the needles at both ends and below. The circuit of CH340T on the right is very complicated. after connecting the power supply and crystal oscillator, the DP and DM of 6 and 7 are connected to the 2 data pins of USB port, and the 3 and 4 pins are connected to the TXD and RXD of our single-chip microcomputer through jumpers.

The 3-pin position of the CH340T circuit adds a 4148 diode, which is a small skill. As a result of STC89C52 this single-chip microcomputer download program needs to start cold, that is, the first click to download and then power on, power on a single chip to detect the need first do not need to download the program. Although the VCC of the single-chip microcomputer is controlled by the switch, but because the 3-pin of the CH340T is the input pin, if there is no such diode, when the power is off, the 3-pin of the CH340T is connected with the P3.0 (that is, RXD) pin of the single-chip microcomputer, and the current will flow into the circuit of the later stage through this pin and charge the capacitor of the later stage, which forms a certain voltage of the later stage, which is as long as two or three volts. However, it can affect the normal cold start. With the addition of diodes, on the one hand, it does not affect communication, and on the other hand, it can eliminate this adverse effect. This central can be temporarily understood, if everyone makes this kind of circuit, you can refer to it.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.