What is JTAG?

JTAG (joint text Action Group: joint test action group) is a 1985 standard for detecting pcb and IC chips, modified in 1990 to become a IEEE standard, namely, IEEE1149.1-1990. Through this standard, the hardware circuit with the JTAG interface can be used for border scanning and fault detection. For chips with JTAG interfaces, the corresponding JTAG pins are defined as: TCK is the test clock input; TDI is the test data input, data is input through the TDI pin JTAG interface; TDO is the test data output, data is output from the JTAG interface through the TDO pin. TMS is selected for the test mode. TMS is used to set the JTAG interface to be in a specific test mode. trst is the test reset, and the input pin is effective at a low level. Gnd
JTAG was initially used to test the chip. The basic principle is to define a tap (Test Access Port & #0; Test Access Port) inside the device) use a dedicated JTAG test tool to test internal nodes. JTAG testing allows multiple devices to be connected together through the JTAG interface to form a JTAG chain, which can be used to test each device separately. Currently, the JTAG interface is often used to implement ISP (In-System rogrammable & #0; online programming) and program flash and other devices.
The JTAG programming method is online programming. In the traditional production process, the chip is pre-programmed and then installed on the board. Therefore, the simplified process is fixed to the board and then programmed with JTAG, this greatly accelerates the project progress. The JTAG interface can be used to program all components inside the PSD Chip.