SLAU358Q September 2011 – October 2019
Answer: Single wires are a poor type of connection and provide very bad quality. Single wires work like inductors connected between the MSP-GANG and target device, generating ripples on the target device side. If a ribbon cable cannot be used, then a twisted-pairs connection should be used instead. One wire on each twisted pair should be connected to a signal connection (for example, TDI or TCK), and the second wire connected to DC (GND or VCC) from both sides of the connection (one on the MSP-GANG side and the other on the target device side). For example, the following arrangement is acceptable:
1 - TDO (Signal wire) - first twisted pair
1 - Vcc / Vcc sense (DC wire)
2 - TDI (Signal wire) - second twisted pair
2 - Vcc sense (DC wire)
3 - TMS (Signal wire) - third twisted pair
3 - RESET (DC wire)
4 - TCK (Signal wire) - fourth twisted pair
4 - GND (DC wire)
If additional protecting components (such as a capacitor or suppressors) are used on the target device PCB, check the JTAG signal shape on the MSP MCU. The JTAG communication speed should be decreased (set to medium or slow) if required. Make sure that any ripple on the JTAG lines is smaller than 20% of the peak-to-peak signal level.
If connection cables are longer than 40 cm, then the ripple can be reduced by inserting 33-Ω resistors in series with TCK, TMS, and TDO in the middle of the connection wires. Do not provide series resistors in TEST and TDI lines if the device will be secured (blown the security fuse) for MSP families 1xx, 2xx, and 4xx. For blowing the security fuse in these devices, the programmer provides Vpp 6.5 V at 100 mA on the TEST or TDI lines to MSP MCU. An additional resistor inserted in these lines can reduce the maximum current provided to the MCU and the security fuse will not be blown.