Build Your Own Jtag

[grynner]

c&p from another site, thanks goes to Xaminator

Build your own Jtag

Building a Simple, Unbuffered JTAG

Parts Required – all available from Radio Shack:

1) 5 pieces – 100-ohm, ¼ watt resistors
2) 1 DB25 male connector with solder terminals in the rear.
3) 14” of 6-conductor ribbon cable or a small spool of insulated 20 or 22 gauge wire, at least 10 feet.

Hint: Find a ribbon cable in your old computer junk box with the header connectors already
attached. The connector needs to be at least 6x2 (supporting 12 pins) while an old IDE ribbon
should also work – though it will overhang the JTAG header quite a bit. Ideally, you’ll find a 10x2
(supporting 20 pins), but these are not very common. Cut the ribbon to about 12 inches – only
one side needs the header connector. The conductor with the red strip indicates the pin 1 wire –
and beside it is the pin 2 wire, on so on.

Tools Required:

1) Fine Tip soldering iron.
2) Small spool of solder.
3) Wire nippers (or cutters).
4) Helpful – wire strippers.
5) Helpful – tweezers or needle nose pliers.
6) Helpful – small vise to hold the DB25 connector while soldering.

Procedure:

Note: A simple JTAG needs to be kept pretty short – about 12” in length or less.


1) If using spooled wire, with wire nippers, cut 6 – 12” foot segments of wire from the spool.
2) Strip about ½” of insulation from each end of each wire segment or each wire of the ribbon.
3) With wire nippers, trim one of each resistor’s two leads to about ½ inch. Save at least one of these
lead trimmings.
4) For each terminal pictured:
a. Holding the long lead of the resistor, solder the short lead to the DB25 terminal.
i. Hold the resistor lead against the DB25 rear terminal, along with a segment of solder.
ii. Heat the terminal with the soldering iron, and let the solder flow into and around it,
surrounding the resistor lead.
iii. Don’t hold the iron against the terminal for more than three seconds – that should be
enough. Any more, and you’ll start melting the housing.
iv. Remove the iron from the terminal and hold the resistor still for a few seconds to
allow the molten solder to cool.
v. This would be easier with three hands. A tech’s trick, usually frowned upon, is to get a
small ball of solder on the tip of the iron, and slowly bring it to the terminal.
5) Using a saved trimming from one of the resistors, solder it across terminals 18-25 of the DB25
connector.
6) Solder a wire segment to the other end of each resistor. Try to get within ½” of the body. Then
trim the excess leads with wire nippers.
7) Solder the last wire segment to the “bar” you created across terminals 18-25.
8) Finished.