Prototype PCB for the ISDN and FXO/FXS interfaces

Posted on 4 May 2010 in Hardware by xcarcelle

the prototyping of the different fonctionnal bloc of the PCB and namely the interaction between the CPU and the Telco interfaces (ISDN and FXO/FXS).In order to do a clean prototyping, it is usually adviced to use the different EVB (EValuationBoards) and SDK (Software Development Kits) supplied by the chip manufacturer (CPU, ISDN, FXO/FXS) and try to do the "proof-of-concept" of the hardware design connecting the different EVBs and use the SDKs provided to run the SPI and TDM buses (Master and Slaves) from the CPU.

In our case, we made some intermediate PCBs that can make a clean connection between the CPU EVB and the ISDN and FXO/FXS interfaces. With the great help of Mehdi Khairy (that used to work with me on the OpenPattern project) using KiCAD to route the different PCBs (some bugfixes sent to the KiCAD bugtracker during the routing at

The ISDN connection from the CPU EVB to the ISDN EVB chip (XHFC-4SU - a 4 T1 lines ISDN frame buffers on-chip from CologneChip) is done using the following PCB (XHFC-4SU-Protoboard) ;


The FXO/FXS connection from the CPU EVB to the FXO/FXS EVB chip (VE890 EVB from Zarlink implementing 2 FXS and 1 FXO) is done using the following PCB (Zarlink-VE890-Protoboard) ;


Next posts will be presenting the results and the signal obtained on the SPI and TDM buses from a Digital Oscilloscope and from a Logic Analyzer (like the saleae one),