Sunday, September 2, 2018

96Boards - JTAG and serial UART configuration for ARM powered, single-board computers

The 96boards CE specification calls for an optional JTAG connection. The specification also indicates that the optional JTAG connection shall use a 10 pin through hole, .05" (1.27mm) pitch JTAG connector. The part is readily available on most electronics sites. Breaking out the pins with long wires and shrink wrapping them is ideal for making sure that each connection is labeled and separate when connecting to a JTAG debugger. While a JTAG connection is not required for flashing or loading the bootloaders onto the board, the JTAG connection is useful for advanced chip-level debugging. The serial UART connection is sufficient for loading release or debug versions of bl0, bl1, bl2, bl31, bl32, the kernel, and userspace.  Last but not least, ARM-powered boards, with 12V power input, often require external fans to keep the board cool. As seen in the below photos, two 5V fans were powered from an external power supply. Any work on microcontroller boards should be performed on a grounded surface.  Proper grounding procedures should always be followed as most microcontroller boards contain ESD sensitive components.

In the below photos, a 96Boards SBC is mounted on an IP65, ABS plastic junction box for durability. The pins are extended and mounted with screws underneath the junction box. The electrical conduit holes on the side of the junction box are ideal for holding small, project fans. The remaining electrical conduit holes provide a clean place to place the remaining wires from the board - micro USB, USB-C, and 12V power.