TG16:Region Information

The PC Engine/TurboGrafx-16 hardware can be easily divided into the two separate regions of their primary releases, Japan and North America.

HuCards
Although identical in appearance, both PCE and TG-16 HuCards are not compatible with each other, which is rather unfortunate as the PCE library is much larger and more affordable than the TG-16's. As a form of hardware lockout, NEC swapped the data bits around on the TG-16 HuCard relative to the PCE (D0 on the PCE is D7 on the TG-16 and so on). In addition, TG-16 HuCards check whether or not pin 29 of the HuC6280 CPU is connected to ground. If not, the game will not boot, preventing TG-16 HuCards from booting on a PC Engine even if the pins for the data bits are swapped around.

Thankfully, several region mods exist and there are also HuCard converters which allow different region HuCards to be played on a PCE or TG-16. On all region mods and most converters, pin 29 of the HuC6280 on a PC Engine must also be wired to ground in order for US HuCards to pass the boot check. Only one HuCard converter, the Turbo PC-Henshin from dB-Electronics, can boot any region HuCard on any region console without requiring this modification.

CDs
CD games can be played on either region console so long as the proper system card is present. However, CD system cards are region locked in the same manner as HuCard games. This is particularly a problem for TurboGrafx-CD owners as the US Super System Card 3.0 (required for Super CD-ROM2 games) is extremely rare and the Arcade Card never saw a US release.

Links
https://nicole.express/2020/trademarks-and-region-locks-engine.html