Mask register CPU1
| CH1OM | processor 1 Receive channel 1 occupied interrupt enable |
| CH2OM | processor 1 Receive channel 2 occupied interrupt enable |
| CH3OM | processor 1 Receive channel 3 occupied interrupt enable |
| CH4OM | processor 1 Receive channel 4 occupied interrupt enable |
| CH5OM | processor 1 Receive channel 5 occupied interrupt enable |
| CH6OM | processor 1 Receive channel 6 occupied interrupt enable |
| CH1FM | processor 1 Transmit channel 1 free interrupt mask |
| CH2FM | processor 1 Transmit channel 2 free interrupt mask |
| CH3FM | processor 1 Transmit channel 3 free interrupt mask |
| CH4FM | processor 1 Transmit channel 4 free interrupt mask |
| CH5FM | processor 1 Transmit channel 5 free interrupt mask |
| CH6FM | processor 1 Transmit channel 6 free interrupt mask |