XIRCREG40_TXST1
tx_status |= GetByte(XIRCREG40_TXST1) << 8;
PutByte(XIRCREG40_TXST1, 0);
PutByte(XIRCREG40_TXST1, 0x00); /* TEN, rsv, PTD, EXT, retry_counter:4 */