2.1.1 MSP430 JTAG Restrictions (Noncompliance With IEEE Std 1149.1)
The JTAG pins are shared with port functions on all devices with a TEST pin. This includes the 5xx, 6xx, and FRxx families as well as certain device groups from the 2xx and 4xx families (see Table 2-14). On these devices, a special entry sequence must be sent to enable 4-wire JTAG connection. This sequence is described in Section 2.3.1.1.
The MSP430 device must be the first device in the JTAG chain (because of clocking on TDI and JTAG fuse check sequence).
Only the BYPASS instruction is supported. There is no support for SAMPLE, PRELOAD, or EXTEST instructions.
The REP430 Software Implementation described within this document should not be
used along with real time operating systems (RTOS) or an interrupt system, as
this could interrupt the programming using JTAG or SBW, in particular the IR/DR
shifts and the TCLK clock generation.