Test messaging and control circuitry coupled to power pad
The present disclosure describes a novel method and apparatus for using a device's power and ground terminals as a test and/or debug interface for the device. According to the present disclosure, messages are modulated over DC voltages applied to the power terminals of a device to input test/debug messages to the device and output test/debug messages from the device. The present disclosure advantageously allows a device to be tested and/or debugged without the device having any shared or dedicated test or debug interface terminals.
1. An integrated circuit comprising:
A. a power terminal and a ground terminal accessible to outside the integrated circuit;
B. functional circuitry having functional input and output leads and having power and ground leads coupled to the power and ground terminals;
C. test circuitry having test leads connected to the functional circuitry and having a dedicated device test output lead extending from the test circuitry, the dedicated device test output lead being free of the functional input and output leads;
D. test messaging and control circuitry having an output lead and having an input lead connected to the dedicated device test output lead;
E. modulation circuitry having an output coupled to the power terminal and an input connected to the output lead of the test messaging and control circuitry; and
F. filter circuitry connected between the power terminal and the power lead of the functional circuitry.
2. The integrated circuit of claim 1 including a capacitor connecting the power terminal to the output of the modulation circuitry.
3. The integrated circuit of claim 1 in which the filter circuitry includes an inductor connected in series between the power terminal and the power lead of the functional circuitry, and a capacitor connected between the connection of the inductor and functional circuitry and the ground terminal.