Specifications

9 March 1999 – Subject To Change Functional Description 4–9
ISA Bus Devices
4.3.2 Utility Bus Memory Device
The AlphaPC 164LX Ubus drives a flash ROM memory device. The flash ROM
chip provides 1MB of flash memory for operating system support.
Flash data is accessed through 20 address inputs. The low-order 19 address bits are
driven by ISA bus sa<18:0>. The high-order 20th bit (flash_adr19) is driven by the
Ubus decode PLA. Address bit flash_adr19 can be changed by writing to ISA I/O
port x800.
The +12 V is applied to the flash ROM by means of jumper J28 so that code updates
can be accomplished, if desired.
4.3.3 ISA Expansion Slots
Two ISA expansion slots are provided for plug-in ISA peripherals (J30 and J31).
4.3.4 ISA I/O Address Map
Table 4–1 lists the AlphaPC 164LX ISA I/O space address mapping.
Table 4–1 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 (floppy)
3BC-3BF Parallel port—LPT1
3F0-3F7 Primary diskette (floppy)
3F8-3FF Serial port—COM1