22
Interrupts and ISA Bus Addresses
6.2 ISA I/O Address Map
Table 25 lists the AlphaPC 164 ISA I/O space address mapping.
6.3 Flash ROM Address Map
The address range for the flash ROM is FFF8.0000–FFFF.FFFF. Flash space of
1MB is obtained by double mapping this 512KB space. FLASH_ADR19 register at
I/O location 800h provides this function. Writing a 0 to this location enables the
lower 512KB of flash. Writing a 1 to this location enables the upper 512KB of flash.
Table 25 ISA I/O Address Map
Range (hex)
Usage
000-00F
8237 DMA #1
020-021
8259 PIC #1
040-043
8253 timer
060-061
Ubus IRQ12 and NMI control
070
CMOS RAM address and NMI mask register
080-08F
DMA page registers
0A0-0A1
8259 PIC #2
0C0-0DF
8237 DMA #2
2F8-2FF
Serial port—COM2
370-377
Secondary diskette
3BC-3BF
Parallel port—LPT1
3F0-3F7
Primary diskette
3F8-3FF
Serial port—COM1
800
FLASH_ADR19 register
801
AlphaPC 164 configuration register
804-806
PCI interrupt registers
