SPJ Systems’ JTAG Cables for ARM

What is JTAG Cable?

All ARM micro-controllers include a JTAG interface port for debugging. The JTAG interface essentially includes 4 signals – TMS, TDI, TDO and TCK. A computer program – like SDB Debugger – can connect to the ARM micro-controller through this JTAG interface. The problem is that computers do not have a “JTAG Interface Port”. Computers typically have I/O ports like Serial port or USB port. So we need a device which will serve as an interface between Computer’s USB or Serial port and the ARM micro-controller’s JTAG port. This device is JTAG Cable.

How does it work?

JTAG Cable is not merely a bunch of wires – though the word “Cable” is likely to indicate so. Actually it includes an active Electronic circuit. It provides JTAG interface on one side and either USB or RS232 (serial) interface on the other side. Physical connection is typically as shown in this figure:

Of course, there are 2 models of SPJ Systems JTAG Cables:

· SJT-S: provides serial port on the computer side.

· SJT-U: provides USB interface on the computer side.

Both provide JTAG interface on the target side.

Many ARM target boards provide standard 20 pin JTAG connector, while some others provide somewhat different kind of connector – typically smaller connector due to space constraints. For example, most of the MiniARM Evaluation boards provide a 10 pin connector. Hence, SPJ Systems JTAG Cables (SJT-S as well as SJT-U) provide 2 types of connectors on the target side: one that is compatible with the standard 20 pin JTAG connector, and another one compatible with the MiniARM JTAG Connector.

If your ARM micro-controller based target hardware provides standard 20 pin JTAG connector, then SJT-S or SJT-U can directly connect to it. If your target hardware provides different pinout for the JTAG connector, then you may need to use an intermediate cable to match the pinout.

Connections of standard 20 pin JTAG connector:

Signals RTCK, DBGRQ and DBGACK are not mandatory.

Connections of MiniARM style 10 pin JTAG connector:

Signal RTCK is not mandatory.

Along with the SDB Debugger, these JTAG Cables can be used for debugging as well as for flash programming.

Have questions? Goto FAQ page.

We also make general purpose evaluation boards, based on ARM micro-controllers (for example, LPC2104, LPC2138, LPC2148…).

Note: We reserve the right to change specifications of any product without notice.