Re: [N8VEM-S100:2269] Re: Jumpers on Z-80 CPU Card

Subject: Re: [N8VEM-S100:2269] Re: Jumpers on Z-80 CPU Card

Date: Mon, 20 Jan 2014 19:30:40 -0800 (PST)

In-reply-to: <006101cf15ef$9b6b9600$d242c200$@YAHOO.COM>

References: <85ac3593-ccbb-43fe-a97e-e9d48da492dd@googlegroups.com> <22348a7a-937f-48a6-a151-e2fcc7b6b4c2@googlegroups.com> <006101cf15ef$9b6b9600$d242c200$@YAHOO.COM>

I'm continuing to have issues trying to access the 32K ROM / RAM on the MSX2 Utility board. There seems to be a pretty basic issue with the design. The 8255 A port need to be configured to enable slot 0 where the EPROM and RAM are mapped. To configure the 8255 I need to be able to run code in the EPROM; I can't however access the EPROM because the 8255 isn't configured.

Any suggestions?

-Neil

Interesting request Neil. Never tried that one. What exactly are you trying to do. Do you want to boot from an external ROM at 0H or somewhere else.
There probably is a way to fool the Z80 to boot externally. Remember U18 forces NOP's on the bus (up to the required boot address). I think if you remove it (and the ROM itself) you may end up booting from 0H. However never tried that. Let's know how it works out.

John