V=value1
Queue 0 Backup Register
| REQCHNR | Request Channel Number |
| RF | Refill |
| ENSI | Enable Source Interrupt |
| EXTR | External Trigger |
| V | Request Channel Number Valid 0 (value1): Backup register not valid 1 (value2): Backup register contains a valid entry. This will be requested before a valid entry in queue register 0 (stage 0) will be requested. |