HiMedia HD300A (RTD1073) TTL Serial Pinout

The other day I ordered one of those HD (which is conveniently capable of standing for both High Definition and Hard Drive) media player boxes. After roughly 2-3 years in the market, such products have really come a long way and matured significantly in both hardware and software, and more importantly, at least for yours truly, the prices have dropped even more significantly, :)

The model I decided on buying is a rather old one, HD300A from HiMedia based on Realtek’s RTD1073 Soc, which is still very popular among both vendors and consumers despite its comparatively old age. Like most Soc’es used in HD media players, RTD1073 is mostly proprietary. Almost all RTD1073-based products run firmwares modified from the same Realtek SDK, although the SDK seems to have been updated once or twice, maybe even more, over the time. Sources for parts of a particular version of SDK are available here and there on the net, but the most vital parts, video and audio en/decoding, are still only available as binaries.

RTD1073-based boards, and other Realtek Soc-based HD media player boards, are highly similar in general. Here is what mine looks like:

HiMedia HD300A Board
HiMedia HD300A Board

The six-pin socket at the bottom behind the IR window is for two TTL serials, as is the case on similar boards. However, the pinout pattern is slightly different, so I think I might as well document it here:

HiMedia HD300A TTL Serial Pinout
HiMedia HD300A TTL Serial Pinout

The serial interface runs at 115200 in both YAMON and Linux, and there is no obfuscation of YAMON commands, which has been reported for certain Realtek-based products from certain vendors. The HD300A comes equipped with a ‘Rescue Flash’ button, so all this is of less use for common users than hackers. I know I will try some stuff soon enough, :)

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