User`s guide

3.5 ISA Bus Devices

3.5.4 Utility Bus Memory Device

The EB164 utility bus (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 PAL. 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 J14 so that code

updates can be accomplished, if desired.

3.5.5 ISA Expansion Slots

Three ISA expansion slots are provided for plug-in ISA peripherals. One of the

slots is shared with the 64-PCI and can be used for a PCI or ISA device.

3–12 Functional Description