Bi-directional TMS lead carrying TMS and frame data in/out signals
The present disclosure describes using the JTAG Tap's TMS and/or TCK terminals as general purpose serial Input/Output (I/O) Manchester coded communication terminals. The Tap's TMS and/or TCK terminal can be used as a serial I/O communication channel between; (1) an IC and an external controller, (2) between a first and second IC, or (3) between a first and second core circuit within an IC. The use of the TMS and/or TCK terminal as serial I/O channels, as described, does not effect the standardized operation of the JTAG Tap, since the TMS and/or TCK I/O operations occur while the Tap is placed in a non-active steady state.
1. An integrated circuit comprising:
A. a test clock lead;
B. a bi-directional test mode select lead for carrying a TMS in signal, a frame data in signal, and a frame data out signal;
C. data circuitry having a frame data input and output connected to the test mode select lead and having control inputs; and
D. state machine circuitry having inputs coupled to the test clock lead and to the test mode select lead, the state machine circuitry having control outputs coupled to the control inputs of the data circuitry.
2. The integrated circuit of claim 1 in which the state machine circuitry has the states of RunTest/Idle, Shift-DR, Shift-IR, Pause-DR, and Pause-IR.