Spy-Bi-Wire is a serialised JTAG
protocol developed by Texas Instruments for their MSP430 micro controller
In this protocol only two connections are used instead of the usual four pins for the general JTAG
interface. The two connections are a bidirectional data output, and a clock. The clocking signal is split into a period of three clock pulses, for each clock pulse the TDI, TDO and TMS signals are passed on the micro controller via the bidirectional data output.
"MCU debug on a pin-count budget"MSP430™ Programming Via the JTAG Interface