I have also built a Floppy drive IF board based on the OSI one, itself copied from Elektor's Junior Computer Nov/Dec 1982.

Not sure this is true as the OSI FD controller (the 610 board) was available in 1979 (when I got mine). I'm sure it was available back in 1978 too.

My grammar was a bit ...

Well we have moved on a fair way from my last post. I have my Floppy Disk Interface PCB up and running and supporting Goteks and real 5.25 drives. I have been able to create .HFE images that boot perfectly in the Gotek and re-created Master OS65D3.1 and OS65D3.3 Floppies too. I even have the ...

Hi BigEd. Thanks for your reply. I think I might load the whole DOS image of the appropriate .65D file from the WinOSI guys resources, load it via the serial port and use it to initialize and write to a new disk.

I'll post how I get on..

I am hoping someone way cleverer than me can help me with a slight problem I have. For some time now I wanted to build a 6502 based dev board similar to an OSI Superboard/UK101. Back in the day I built a UK101 and attached a Floppy to it very successfully. I have the 5.25 floppies from then (1985 ...

SRAM pins:-
27(/WE) RamRW
22(/OE) RomOE
20(/CS) A15
RamRW is derived from /CPURW NANDED with Phi2
RomOE is derived from CPURW NANDED with Phi2

You cannot use A15 as a chip select for reasons that have been highlighted already, several times. A15 can remain 0 or 1 for many cycles and therefore ...

SRAM pins:-
27(/WE) RamRW
22(/OE) RomOE
20(/CS) A15
RamRW is derived from /CPURW NANDED with Phi2
RomOE is derived from CPURW NANDED with Phi2

You cannot use A15 as a chip select for reasons that have been highlighted already, several times. A15 can remain 0 or 1 for many cycles and therefore ...

Chip Enable: /CE selects the device when low. Asserting /CE low causes the
address to be latched internally. Address changes that occur after /CE goes low
will be ignored until the next falling edge occurs Thanks, John. Paul, in case this isn't clear it means /CE will need to be qualified with Phi2 ...

I used an FM1808 in 2004 for this : http://www.zeridajh.org/hardware/gommc/index.htm .

You have to take special notice of this (see the datasheet) :

Chip Enable: /CE selects the device when low. Asserting /CE low causes the
address to be latched internally. Address changes that occur after /CE ...

Hi. I have built a 6502 dev board containing a WD65C02, 6850,27C256 EPROM,HY62256 SRAM and various decoding logic. I want to replace the SRAM with Ramtron FM1808 in order to retain programs when power is off. I have tried numerous combinations of OE/CE/WE tied low, connected to R/W etc to no avail ...

Hi Dave,
Could i take you up on your kind offer of the OSI modified assembler you run on your PC please? It would certainly help me assembling the source you very kindly supplied for the original OSI assembler so i can have it in ROM on my DIY 6502.

Kind Regards,

Paul

Hi Dave,
Apologies for not replying sooner...only just seen your post. Thanks for this. I'm hoping to re-assemble so it sits in my spare rom space. Is there any chance you could share your PC version of the OSI Assembler. That would be awesome.

Kind Regards,
Paul

Thank you so much for all your help and brilliant explanations chaps. It really does help to understand what is going on in order to get the right result.
KRs
Paul

Well thanks to your considerable help I now have a source file that assembles albeeit with 10 Warnings regarding changed values on the 2nd Pass. I've checked out the byte values in those locations and the assembly is correct so a good result there. btw the -OP00/256*256+OP00 worked a treat. Those ...

Thanks again guys. Managed to get a clean Pass 1 then Oh dear...425 Errors..Mainly Sync errors and I think they are just where lots of .BYTE Lines are not generating code. They are failing on 2nd Pass as *Error* Operand field size error, so I guess we are back to our Low/High byte issue. Taking out ...

Hi BigEd,
Well that solved the Hi Byte Lo Byte issue. Thank you. I now have *Error* Invalid operand Field and it occurs in 8 lines where we have .BYTE and a label with a ? preceding it. Nothing in the A65 manual mentions a specific case for a label with a question mark at the beginning.... Line 867 ...