*** M E M O R U M ***

OK, so I was stating the obvious :oops: However, assuming that I am looking at the latest version of the circuit diagram (Video Board 1.02.pdf) then it appears that at present the VDP wait output is just connected to the Z80 wait input. It is not clear to me from the data sheet of the V9958 (also fr...

Dave wrote (http://primrosebank.net/computers/mtx/projects/mtxplus/mtxplus.htm): 31/01/2015...trying to find (with help) a hardware solution to allow the VDP on the video board to be written to at any CPU speed... Sounds to me like you need a wait state generator. Zilog publish a circuit using a 74x...

Dave is now hosting my note on his site at http://primrosebank.net/computers/mtx/mtxmanuals.htm#node . I have just sent him an update, which will hopefully appear in due course. I think this largely completes documenting the on the wire protocol. There is still a lot of work to be done to document a...

Dave, One thing that might be worth trying: create a ROM that is the same as the standard NODE ROM, but with the initial 8 byte auto-run signature (87654321) replaced by something else (e.g. 00000000). The MTX should then ignore the ROM on power up, and boot normally. You should then be able to acti...

Dave, Yes, please do host my note on your site. I did think before I posted my last that that would be a better solution than cluttering the forum. You should mention that my note is building on the ROM disassembly provided by Tony Brewer. Also, it is still very much a work in progress. Understandin...

Not much added to the disassembly, but rather more detail on the on the wire protocol. I have discovered an undocumented limitation in the NODE SEND and RCV commands. The names of the variables sent and received must be no more than 8 characters, otherwise you receive an "Out of Range" err...

Success at last :D A working Oxford Ring joining two computers over serial. I cannot quite claim RS232, as it is actually using 3.3v logic levels. Ring_Demo.jpg The (emulated) CTC was receiving interrupt acknowledge when interrupts were disabled and was then masking the RETI from the emulated DART. ...

Wile the Z80 emulator Andy uses for MEMU is good in most respects, it is not quite ideal with respect to interrupt handling. By default it has a latency of up to 1000 cycles (although the undocumented -iperiod switch can be used to reduce that). Also, there is no real interrupt acknowledge cycle, in...

Tony, Have not tried that yet. My understanding was that the NODE BAUD command set the baud rate for channel 2, not for the ring. As you suggest, editing LDCNST to return a high value might be better. However, if I resort to that, it will never interoperate with a real MTX, not unless that also has ...

I am beginning to think that my original objective is not possible. It looks as though it may not be possible to create an Oxford ring over serial with MEMU running in user space. For testing, I switched to using an RPi as one node, using the inbuilt serial port, and my laptop with a USB to 3.3v TTL...