The ICEconnect Emulation Interface

The Problem

All new high performance microcontrollers and microprocessors like the C166 family are now released in packages of 100 to 200 pins. Coupled with small size, the pin pitch is typically 0.635mm and as the devices are always surface mounted, the pins are short.

Most projects go straight to a surface mounted prototype with the CPU soldered in, so in-circuit emulation must be performed via clip-overs costing around £500-£800. Siemens have designed the SAB80C166 family to recognise the presence of the clip-over and subsequently put all pins into a high impedance tri-state, to allow On-Circuit Emulation (ONCE). Thus the soldered-in CPU is dormant.

Older package types such as PQFP have bumpers at the corner on to which clip-over can be anchored quite effectively. Clip-overs for newer package types like the bumperless MRFP rely on sprung contacts being compressed around the perimeter of the device by a sliding locking ring. This is at best temperamental and usually unreliable after extended use. The connectors themselves are easily damaged during storage due to the long and exposed nature of the pins.

Clip-overs are by definition sacrificial parts which is unacceptable in view of their high cost. Some existing C166 users have already originated various ways of by-passing the troublesome clip-over by bringing the signals required for emulation out on a special connector or additional row of pads around the CPU.

The Solution -ICEconnect166

Now to try and standardise these clip-overless connection methods, Hitex have defined an emulation interface for the 80C166 family which does not involve clipping onto very fine CPU pins. The new interface does not rely on the ONCE mode employed by the existing clip-over as it is the soldered-in CPU which actually performs the emulation. If new 80C166 users include a Hitex-supplied 2 x 40 way connector with a signal arrangement according to the ICEconnect specification, then a low cost and emulation probe can be used. For mass production, the ICEconnect socket is removed. The only overhead on the design is a row of pads 35 x 4 mm in area.

By using the soldered-in CPU as the emulation device, a number of other benefits follow such as reduced disturbance of port lines due to there being no extension of signal paths. This is particularly important for A/D convertor inputs as clip-overs can quite easily add one or two bits of uncertainty to the C166's 10 bit A/D convertor. The mechanical integrity of the connection is considerably higher than a clip-over and is rated at around 1000 cycles.

The ICEconnect socket can be used as an end-of-line test port to allow the bus integrity to be verified. It also allows alternative test code to be presented to the soldered-in CPU, overriding any application code installed on the board.