There are two distinct variants of the Multi-ICE unit in existence; the original 'Model 82' and the newer 'Model 83'. (The model number is printed on the bottom of the Multi-ICE case.) Both types will work with the same versions of the Multi-ICE Server software, but there are some differences in the design of the hardware. This FAQ covers only the differences in the power supply requirements. For information about other hardware differences, please see: 'Differences between the two versions of Multi-ICE hardware'.

The Model 83 unit can be powered from one of two sources:

a) From the debug target's power supply via pin 2 (Vsupply) of the JTAG cable, provided this supply rail is between 2V and 5V DC, with a minimim of 500mA spare current capacity. (See 'Current requirement on power-up').

b) From an external power supply via the Multi-ICE's 2.1mm DC input jack socket, which is located next to the JTAG cable connector. Acceptable parameters for this input are: 5V to 9V DC, minimum 500mA available, center pin positive.

The Model 83 Multi-ICE has separate, internal switch mode power supplies for the Vsupply input on the JTAG cable, and the DC in jack socket. These power supply circuits are of a different design and hence have different input voltage ranges.

The Model 82 unit can only be powered via the JTAG cable, as described in 'a)' above. In the event of connection to a board where the Vsupply pin is not connected or cannot deliver sufficient power, an external power supply must be connected. This requires a minor wiring modification to 'inject' an external power supply into the JTAG cable.

This can be realized by several methods, e.g. Building a custom JTAG cable, Using the 14 to 20-way adapter plug that was sometimes supplied with Multi-ICE (only useful if your target has a 14-way JTAG connector), or by 'cutting and splicing' external power supply wires into the existing JTAG cable. The latter is generally the quickest solution, but would invalidate any warranty remaining on the supplied JTAG cable. The diagram below shows the connections that should be made:

If you use an external power supply with either model of the Multi-ICE hardware, you can debug targets with logic voltages of 1V to 5V. The Multi-ICE unit senses the target logic voltage using pin 1 (VTref) of the JTAG connector, and adjusts its input threshold and output drive levels to suit.