I got a general question about the history of JTAG. From what I gather, JTAG was first made to test the integrity of the joints on an assembled PCB (boundary scan) with no debug or programming in mind.
But then later on, chip manufacturers added in extra circuitry that was used for in-circuit programming as well as debugging. This circuitry was made to use the JTAG serial port as a point of access since it was already there?
Is this correct? THe JTAG specifications was originally designed for boundary scan so the way of going about this is pretty much common among all the processors. But since the JTAG port is a serial interface manufacturers added additional circuitry that interpreted the JTAG signals differently to allow other functions like programming/debugging. But these additional functions were added by individual manufacturers after the fact so the software protocal for them is not common among the processors.
??
But then later on, chip manufacturers added in extra circuitry that was used for in-circuit programming as well as debugging. This circuitry was made to use the JTAG serial port as a point of access since it was already there?
Is this correct? THe JTAG specifications was originally designed for boundary scan so the way of going about this is pretty much common among all the processors. But since the JTAG port is a serial interface manufacturers added additional circuitry that interpreted the JTAG signals differently to allow other functions like programming/debugging. But these additional functions were added by individual manufacturers after the fact so the software protocal for them is not common among the processors.
??
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