Utility Bus Memory Device; Isa Expansion Slots; Isa I/O Address Map - DEC AlphaPC 164LX Technical Reference Manual

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)
000-00F
020-021
040-043
060-061
070
080-08F
0A0-0A1
0C0-0DF
2F8-2FF
370-377
3BC-3BF
3F0-3F7
3F8-3FF
22 January 1998 – Subject To Change
Usage
8237 DMA #1
8259 PIC #1
8253 timer
Ubus IRQ12 and NMI control
CMOS RAM address and NMI mask register
DMA page registers
8259 PIC #2
8237 DMA #2
Serial port—COM2
Secondary diskette (floppy)
Parallel port—LPT1
Primary diskette (floppy)
Serial port—COM1
ISA Bus Devices
(Sheet 1 of 2)
Functional Description
4–9