exxos's Atari, Amiga & retro forum

Maximilian wrote: 24 Jan 2020 01:15 Didn't know the schematics from the FMV were online.

You are right, there is a switch in the STV8438CV for Amiga / C-Cube output.

Does that mean Ext_Video is always low if an FMV unit is placed?, makes sense....
Could not find it in the crappy PDF schematics i found , maybe there are better ones out there?

I was able to get the ESM up on the DB23 with the FMV in place. So probably not always low?

Someone was kind enough to send me this on another forum when i was digging for info on the FMV card. it's pretty interesting, a presentation by the main engineer on the FMV stuff, starting with the CDTV which should have been a prototype for the CDTV-CR, instead of the CDTV being released and the CDTV-CR getting shelved, then the CD32 and FMV development on from there, through to the prototype CD1200 and the fun with that.



so as i can figure, the FMV card switches off the normal amiga output to the composite and s/vhs encoder, and routes the normal amiga analogue RGB into itself. it then does the video mixing into colour 0 and routes the whole lot back into the amiga's video encoder.

no funky stuff happens on the amiga side, all it's good for is overlaying buttons and control stuff on screen - as much as i understand it

Thanks.

Judging by the setup the FMV doesn’t pass this back to the edge connector. I guess they never expected anyone to put a DB23 on the riser. Either way I think the answer is to replicate the switch on the riser

Think i've had an epiphany.

On the riser we should be using EXT_AR, EXT_AG, EXT_AB with appropriate passives.

This would pick up the standard video when U36 is ON.

This would pick up the FMV + Mixed Video when U36 is OFF.

terriblefire wrote: 31 Jan 2020 10:15 Think i've had an epiphany.

On the riser we should be using EXT_AR, EXT_AG, EXT_AB with appropriate passives.

This would pick up the standard video when U36 is ON.

This would pick up the FMV + Mixed Video when U36 is OFF.

Can someone explain "appropriate passives " that have to be on the EXT_AX signals, please ?

Rochabian wrote: 20 Sep 2025 08:22 Can someone explain "appropriate passives " that have to be on the EXT_AX signals, please ?

Look up transmission line load impedance. It entirely depends on your application.

terriblefire wrote: 21 Sep 2025 13:54

Rochabian wrote: 20 Sep 2025 08:22 Can someone explain "appropriate passives " that have to be on the EXT_AX signals, please ?

Look up transmission line load impedance. It entirely depends on your application.

I mean what are the passive components that have to be added to those signals to make a riser with a DB23 video output that is capable to output FMV+video on the DB23 ? Diodes, capacitors, resistors ? Between wich signals ?

Can someone do a simple scheme on how to do that (if it's simple of course ;) )?

No the riser needs redesigned

I understand that the riser should be redesigned, like a promodule riser for example.

What are the necessary modifications, if we take the example of the promodule riser, wich has no component on it (not even passive components) , to be able to use FMV + TF330 if i just want to add a DB23 on the promodule riser ?

OK, i understand.

I have to make a switch to route on the DB23 the AR AG AB signals if no FMV or the AR_EXT AG_EXT AB_EXT if FMV is present

The presence or not of the FMV is given by the EXT_VIDEO signal value

Using a 74HC4066D on the riser is the easiest way ?

EDIT: As Stephan said before we can just use AR_EXT AG_EXT & AB_EXT because when FM is not present AR_EXT=AR AG_EXT=AG & AB_EXT=AB

So we just need to adjust the AX_EXT signals levels with passive

I understand quickly but it takes a long time to explain to me :shock: