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# MD398 Reverse Engineering
Resources for the Tytera (TYT) MD398 (aka Radioddity GD-55).
## General Information
The radio uses a vastly different design than the familiar MD380/MD390. It uses the [AT1864S radio SoC ](http://www.auctus.cn/enindex/ptshow.html?id=2 ).
It is a familiar chip used in many Wouxun/Baofeng model, however to the key difference that this
newer S series provides an IQ baseband interface.
It appears to be using an integrated ARM M7 built into the HR-C3000.
The programming cable is actually a common USB to TTL serial interface (**not** an actual USB device).
It's still not impossible the radio could appear as a DFU usb device for uprgades however.
## Boot Modes
Different boot modes seem to be available:
| PTT | TOP SIDE BUTTON | BOTTOM SIDE BUTTON | EMERGENCY BUTTON | Function |
|:---:|:---------------:|:------------------:|:----------------:| -------- |
| *X* | | *X* | | Flip + Mirror screen |
| | *X* | *X* | | ??? Black screen no chime, upgrade mode? |
| | | *X* | *X* | GPS Test mode |
