JTAG pins order for USB Blaster III - 1.27" header

Hi Zvi,

Yes. For a new board with the USB Blaster III 1.27 mm, 2 × 5 JTAG connector, use the USB Blaster III micro-header pinout, not the older 2.54 mm header order.

For JTAG mode, the pinout is:

Pin

Signal

1 - VCC_TARGET

2 - TMS

3 - GND

4 - TCK

5 - Not connected

6 - TDO

7 - Not connected

8 - TDI

9 - GND

10 - nPROCRST
 

So, pin 7 is not used for JTAG. It is used as nCS only in Active Serial mode.

The 1.27 mm connector was introduced for a smaller cable interface. The included adapter board maps this new pinout to the older 2.54 mm header, which is why the signal order differs from older cables.

For a direct connection, use a keyed 1.27 mm, 2 × 5 male header on the target board and follow the pin numbering shown in the USB Blaster III User Guide. At this time, the adapter-board mapping in the user guide is the available reference for this interface.

USB Blaster III FPGA Development Cable User Guide

Regards,
Fakhrul