External Interrupt Request Register
| ER0 | Bit0 of EIRR |
| ER1 | Bit1 of EIRR |
| ER2 | Bit2 of EIRR |
| ER3 | Bit3 of EIRR |
| ER4 | Bit4 of EIRR |
| ER5 | Bit5 of EIRR |
| ER6 | Bit6 of EIRR |
| ER7 | Bit7 of EIRR |
| ER8 | Bit8 of EIRR |
| ER9 | Bit9 of EIRR |
| ER10 | Bit10 of EIRR |
| ER11 | Bit11 of EIRR |
| ER12 | Bit12 of EIRR |
| ER13 | Bit13 of EIRR |
| ER14 | Bit14 of EIRR |
| ER15 | Bit15 of EIRR |