On 05/25/2012 01:31 AM, ict@ccess wrote:
Although the EPROM is 32 kb, and only 16 kb is needed for the motherboard ROM, I was trying to ascertain if the slot ROMs were also stored on the EPROM. I have 2 EPROMs with different versions of ROM and although the ROM differs slightly between the 2 versions, the slot ROM code remains exactly the same. I thought for sure if the ROM code differed, then at least some changes should have/would have been made also to the slot ROM code. So with this analogy, I surmised that the slot ROM code is not stored on the EPROM but on another on board chip.
The Laser 128 Tech Ref is available in PDF. I found the layout of the ROM in Fig. 11-6. It shows the physical and logical address layout in great detail, along with a description of the hardware decoding :-).
The Slot ROM code is mostly in the upper half of the EPROM and has some very strange aspects. The 3.5" disk code is distributed over 6 1k banks that cover logical address CC00-CFFF. This is not large enough for the UDC image, which appears to require 8k (but also looks like it's divided into 1k banks).
Looks like I have some serious disassembly ahead of me. But, the manual is complete enough in terms of hardware description that it should be at least possible.
What are folks fond of for 6502 disassembly nowadays? It's been years since I've been through an exercise of this type.
Steve