2.3 Constructing a Connector

On most target hardware, the pins are arranged in a 3x2 pin 2.54mm header, similar to Figure 2.4. The pin-out is depicted below in Figure 2.3.

BKGD  1   o  o   2 GND
 -    3   o  o   4 RESET
 -    5   o  o   6 VDDX

Figure 2.3: The typical pin arrangement of the BDM connection

Pin 2 is signal ground. Pin 4 is the reset pin. Taking this pin to ground causes the target micro-processor to reset itself. Pin 1 is a bidirectional serial data pin through which all communication between the controller and target occurs. Pin 6 is the supply voltage from the micro-processor. It is not used by µPad.

Figure 2.4: A BDM connection on a target device

Accordingly you will need a 3x2 IDC header connector, a length of 6-core ribbon cable and a connector appropriate for your chosen controller.

Write down a table describing the physical pin connections at each end of the cable. For example, if you have chosen the pins mentioned in Figure 2.2, then the table would look similar to that below.

Connection

Controller End

Target End

GND

X1,24

2

RESET

X2,3

4

BKGD

X2,5

1

Now is the time for the practical work. Construct a cable according to the table you have recorded. At the target end, the IDC connector should be crimped to the cable as shown in Figure 2.5.

Figure 2.5: The target end of the controller–target cable

The connector at other end of the cable depends upon your chosen micro-controller. An typical example of how it might look is shown in Figure 2.6. As you will not need to change this connection very often, soldering the wires is also acceptable.

Figure 2.6: Cable connection at the controller

It is best if the length of the cable does not exceed 250mm.