Texas Instruments MSP430 manual External Power, Bootstrap Loader BSL

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2.2External Power

The PC parallel port can source a limited amount of current. Because of the ultra-low-power requirement of the MSP430, a standalone FET does not exceed the available current. However, if additional circuitry is added to the tool, this current limit could be exceeded. In this case, external power can be supplied to the tool via connections provided on the target socket modules. See the schematics and pictorials of the target socket modules in Appendix B to locate the external power connectors.

The MSP-FET430UIF can supply targets with up to 100 mA through pin 2 of the 14-pin connector. VCC for the target can be selected between 1.8 V and 5 V in steps of 0.1 V. Alternatively, the target can be supplied externally. In this case, the external voltage should be connected to pin 4 of the 14-pin connector.

The MSP-FET430UIF then adjusts the level of the JTAG signals to external VCC automatically. Only pin 2 (MSP-FET430UIF supplies target) or pin 4 (target is externally supplied) must be connected; not both at the same time.

When a target socket module is powered from an external supply, the external supply powers the device on the target socket module and any user circuitry connected to the target socket module, and the FET interface module continues to be powered from the PC via the parallel port. If the externally supplied voltage differs from that of the FET interface module, the target socket module must be modified so that the externally supplied voltage is routed to the FET interface module (so that it may adjust its output voltage levels accordingly). See the target socket module schematics in Appendix B.

2.3Bootstrap Loader (BSL)

The JTAG pins provide access to the flash memory of the MSP430Fxxx devices. On some devices, these pins are shared with the device port pins, and this sharing of pins can complicate a design (or sharing may not be possible). As an alternative to using the JTAG pins, most MSP430Fxxx devices contain a program (a "bootstrap loader") that permits the flash memory to be erased and programmed using a reduced set of signals. The MSP430 Programming Via the Bootstrap Loader User's Guide (SLAU319) describes this interface. TI does not produce a BSL tool. However, customers can easily develop their own BSL tools using the information in the application reports, or BSL tools can be purchased from third parties. See the MSP430 web site for the application reports and a list of MSP430 third-party tool developers.

TI suggests that MSP430Fxxx customers design their circuits with the BSL in mind (i.e., TI suggests providing access to these signals via, for example, a header).

See FAQ Hardware #11 for a second alternative to sharing the JTAG and port pins.

SLAU278F –May 2009 –Revised December 2010	Design Considerations for In-Circuit Programming	27
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