The Raspberry Pi SOC supports up to 2 PCM channels that it is described in BCM2835 datasheet page 119 which like below diagram
Therefore, we could expanse our 4 ports PiTDM to 8 ports PiTDM if we can use all of its 2 channels, that also means we are using 1 channel for 4 ports PiTDM right now :). The most important challenge is that we need to align the second channel to correct timing of 2M PCM highway. Fortunately, through a half month of hard work, we made it out and the 8 ports PiTDM module is going to release in next month 🙂
Here is a picture which is shown an 8 ports PiTDM is detected by the Digium GUI:
What is it can do of an 8 ports design?
Well, obviously, the 8 ports design can give you more ports which can expanse your PiTDM ability and capability, you can have 8 ports FXO connect to PSTN, or you can have 8 ports FXS connect to your phone or FAX machine.
Also, we can add the BRI module support as we have 8 pure 8bits PCM channels, certainly, we have the ability to support a BRI controller which means we can bring the Raspberry Pi to ISDN world.
The most famous and stable BRI controller is XHFC-4SU in the Asterisk world, here is it’s datasheet link http://www.colognechip.com/isdn/controllers/frame-xhfc-4su.htm