With our experience, serial programming is not as simple as parallel programming because the target load is unknown. Each programming algorithm is customized for most of the cases to suit customer’s PCB design. There are many factors such as length of wires, crosstalk, Power needed by PCB and other adjacent components on PCB which needs to be considered while developing ISP programming algorithm. It is preferable that customer PCB get tested with the algorithm ahead of time and that is the service we always recommend. Substantial engineering resource is needed to support the chip and provide after sales support for ISP programming. Therefore we quote for ISP on case by case basis depending on project complexity.
Other programmer manufacturers may have the ISP chip listed as supported, but there’s a high chance of the chip not functioning properly because the target board has not been tested. When customer pays engineering fees for particular ISP algorithm development, we make sure that the device can be programmed in circuit at customer’s end and help to troubleshoot any issues which may arise in setup. Because of the level of customized support needed for serial programming, the support fees are higher than parallel programming.