Tips for In-Circuit Programming

An adjacent component on a target PCB may interfere while programming chips in-circuit, therefore special attention is needed while designing PCB used for in-system programming (ISP). Xeltek has helped many customers troubleshoot design problems in target PCBs and the following points are important and should be considered while performing ISP or designing a board for in-system programming.

1) Attention to Pin Connections

a) All pins required during programming should have interface terminals or test points to ensure that SuperPro IS01 can be connected easily.

Pins required for programming in the above diagram are all connected to the interface terminals, therefore, it is simple to test and burn chips. Double check connection after connecting the color coded ISP cable to the target board.

b) To prevent pins from incurring signal jump during programming, make sure PCB circuit boards where programming pins are located is not connected with other circuits.

2) Power Precautions

Although Xeltek ISP programmers can provide programming power (1.8-18V, 5W), in most cases, power from the ISP programmer alone is not sufficient for the target board to function normally. All target boards must ensure correct programming voltages determined by the chip specs. When external power supply for PCB is used then VCC from the ISP programmer cable should be left unconnected and Ground of the ISP cable should be connected to Ground of target PCB.

3) Precautions for the Design with Reset Generator

Be extra cautious if the RESET pin is needed during in-system programming and the RESET generator has already been provided on the target board. The RESET generator may conflict with the programmer actuation signal and create issues when driven by the ISP programmer.

A simple solution is to add a jumper on the RESET pin but such operation is not very convenient. A better solution is to add a pull-up resistor on the RESET pin (the best and most recommended solution).

Such connection in the above diagram settles the conflict problem through a pull-up resistance.

4) Length of ISP Cable and Crosstalk

If the ISP cable is too long, there will be programming issues due to timing disturbance. Recommended cable length is 25 cm, but if the user plans to use longer cable, be sure to select medium or low speed in Operation Options of SuperPro software.

A shielded cable is recommended because there may be crosstalk between different signals on the ISP cable. For example with the STM8 series, it's suggested that the SWIM wire be separated from the others.

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