This means, you can solder a lonely SoC to a PCB, no Flash-Chip, no RAM then connect to it via JTAG and interact with the SoC. Because, through the JTAG automate in the SoC, you can also write to the Flash Chip.Ī JTAG port can be used without any software running on the IC itself, but the IC still has to be powered by a separate power supply. But of course it can additionally be utilized to recover a device if you erased the bootloader resident on the flash.
You then run a special JTAG software on your PC, which allows you to comfortably control the JTAG automate and make it perform commands like reads and writes at arbitrary locations.Īs already stated the primary intention of the JTAG automate is to test the IC itself. To do that, you need to connect the parallel port of your PC with the JTAG header on the PCB via a bought or a homemade “JTAG cable”. You can test and program the IC by issuing JTAG commands to it through the JTAG. There is always a JTAG automate (JTAG logic) integrated into your soc or cpu and usually this is connected to a JTAG header on the PCB.
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