Dear Lee,
please pull the STB pin low (to GND) to set the TJA1040 to normal mode.
Then, by pulling the TXD pin low, the CANH and CANL pins will be set to recessive state.
If you want to put the CANH and CANL pins to dominant state, please pull the TXD pin to high state. Minimally above 2V, maximally to VCC+0.3V. The TXD pins has an internal pull-up to the VCC pin. Leaving the TXD pin floating, should also set the CANH and CANL pins to dominant state.
With Best Regards,
Jozef
