Description
The USERCODE instruction can be read out of devices simply by loading the JTAG instruction register with the USERCODE instruction and shifting out the 32-bit code.
Reading the USERCODE instruction out of a device is a relatively simple JTAG process. Below is psuedocode that summarizes the process:
- Traverse the JTAG state machine to the Shift-IR state
- Load the USERCODE instruction
- Traverse the JTAG state machine to the Shift-DR state
- Shift out the 32-bit USERCODE value
The easiest way is to obtain the USERCODE is to use Jam™ Files or Jam Byte-Code Files, especially for embedded systems that already implement a Jam Player. The Jam language provides an easy interface to the JTAG port.
Refer to the device family data sheets for information on which devices support the USERCODE instruction.