Hi Neil The S-100 Utility board design is intended to default to "slot 0" which is the 32KB ROM and 32KB RAM. I take it you cannot see the 32KB ROM with the CPU without code to configure the 8255? If so, then there is a "chicken and the egg" problem. It is the only ROM in an MSX system other than those plugged into the cartridge port. Is the 8255 port A coming up after reset as an input port? If so, it may be possible to add pull-up/pull-down resistors to force a configuration on the port pins even if the 8255 is not initialized. Unfortunately I cannot see the schematic at the moment so I will have to take a look later today and see if I can think of any ideas. If you could run code on CPU from a ROM how would you configure 8255 port A? As an output and with what values on the pins. If port A is an output with 0x00 or 0xFF on it then all we need is a SIP for pull-up/pull-down resistors. Thanks and good luck! I appreciate you taking this project on. I know it is frustrating!
Andrew Lynch From: nbreeden <[email protected]> To: [email protected] Sent: Monday, January 20, 2014 10:30 PM Subject: Re: [N8VEM-S100:2272] Re: Jumpers on Z-80 CPU Card 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 > -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
