FT232AM design circuit and Chinese documentation

1FT232AM Introduction

FT232AM is a USB-RS232 converter provided by FTDI. It can easily establish a reliable connection between RS232 and USB interfaces. The plug-and-play and hot-swap performance of the USB interface provides a very easy-to-use environment for RS232 peripheral devices, and provides a transmission rate of up to 115kb/s (if the level converter uses MAX3245CAI, the transmission rate can reach more than 1Mb/s). At the same time, it also provides a USB-RS422/RS485 port, so that the two communication protocols of RS422/RS485 and USB complement each other, so that the device has both plug-and-play and hot-swap performance and long-distance transmission and anti-interference characteristics.

2.2 Hardware Design

The design circuit of FT232AM is shown in Figure 1. It provides a standard DB-9 pin signal line to the outside. When the PC peripheral is set to RS232 level, MAX3245CAI is used for RS232/TTL level conversion. A 93C46 is also expanded in the design to store the VID, PID, device serial number, etc. of the developed PC peripheral.

2.3 Drivers

In Window98/2000/XP system, user-level applications must access USB hardware devices through drivers. Although many companies currently provide development tools for writing drivers, it is still relatively difficult. When using FT232AM, since FTDI provides a virtual serial port (VCP: virtualCOMport) driver, after installing the VCP device driver, the system virtualizes the USB peripheral into a serial port device (usually COM3), so that the application accesses the USB port just like accessing a standard serial port, and LabWindows/CVI provides a serial port programming function library, so that user program development can be very convenient.

3LabWindows／CVI

LabWindows/CVI is a virtual instrument software development platform for computer measurement and control developed by NI. It provides a wealth of virtual instrument controls and has excellent hardware interface functions. It provides dedicated drivers for almost all data cards, acquisition instruments and other acquisition devices. The RS232 function library provides various serial communication control functions. According to the actual serial communication, it can be divided into 6 categories: opening and closing serial port functions, I/O read and write functions, modem control functions, serial port setting functions, register status functions and callback functions. Some of the more commonly used functions are as follows:

(1) Open/Close function

(2) I/O read and write functions

I/O read and write functions provide a variety of read and write methods, only some of the functions are introduced here.

(3) Modem control function

4. Software Design

The program flow chart of serial communication is shown in Figure 2. Since different acquisition instruments have different communication protocols, it is necessary to write PC programs according to the specific instrument communication protocols. This article will take the communication between PC and USB as an example to illustrate the method of implementing USB communication in LabWindows/CVI. Figure 3 is the program interface diagram of the virtual oscilloscope.

Some of the code in the program is as follows:

(1)Configure and open the serial port

The communication port selection and communication parameter configuration panel is shown in Figure 3. In the callback function of the "Configure" button, configure and open the serial port according to the selected parameters.