GENERAL PURPOSE SERIAL COMMUNICATION USING JTAG INTERFACE

摘要

The present invention relates to a method for operating an electronic device (ED1, ED2, EDn) by means of an IEEE Std. 1149 protocol in an extended functional mode provided for allowing additional serial communication with the electronic device, the method comprising providing at least one of the signals in the IEEE Std. 1149 protocol to the electronic device, the IEEE Std. 1149 protocol including at least one of a mode signal (TMS), a clock signal (TCK), a data input signal (TDI) and a data output signal (TDO), providing at least one duplicate signal (TMS', TCK', TDF, TDO') of the signals in the IEEE Std. 1149 protocol to the electronic device, and setting a state machine associated with the IEEE Std. 1149 protocol in a non-affecting state in which an output signal (TDO) of the IEEE Std. 1149 protocol does not affect the at least one duplicate signal (TMS', TCK', TDF, TDO'), thereby allowing for the at least one duplicated signal (TMS', TCK', TDF, TDO') to be used for additional serial communication with the electronic device (ED1, ED2, EDn). Advantages with the present invention includes the possibility to limit the number of data lines to an electronic device, as it is not necessary to have both a general purpose communications interface and a testing and debugging interface. It is furthermore not necessary to alternate and/or adapt the TAP controller of the JTAG protocol as it is possible to instead set the state machine in the TAP controller to a state in which an output signal of the JTAG interface is kept in a non-affecting state where it is not affecting the general purpose communication. The present invention also relates to a corresponding electronic device.