Citation:
If component is linked to other component that needs incoming data, like TComDataPacket or TCustomComTerminal, OnRxChar event is is not called, however, the component calls OnRxBuf event. The application can not read the data from input buffer inside OnRxBuf event, since it has already been read. The data is placed automatically by the component in Buffer parameter of OnRxBuf event. Whether OnRxChar or OnRxBuf event is called, can be checked with TriggersOnRxChar property.
Donc, essaie avec OnRxBuf. A ce moment, il ne faut plus lire l'octet au même endroit. Tu peux voir comment on fait pour le récupérer dans l'aide.