Lmst

Repórter Retro 106

https://retropolis.com.br/2024/08/28/reporter-retro-106/

#ReprterRetro #6502 #6800 #6847 #ActionRetro #AdrianBlack #Arcade #Asianometry #AugustoBaffa #Baffa3 #CP500 #Cray #CRT #ctrlaltrees #CultOfTheDeadCow #CulturaHacker #DavesGarage #DigitalEquipmentCorporation #EPROM #fliperama #Fofoca #Intel80286 #LaCoCoStrangiato #Lemmings #Macintosh #MC6847 #PDP11 #PicoMEM #PLM #Prottipo #RaspberryPi #RetroRio #RMC #SeymourCray #SPLM #Tatung #Terminal #The6502Show #ValdemarGomes #v

A little more fun with the #MC6847, hooking the lower part of the address bus to the device's data bus, instead of hardcoding a single value on it, so that it cycles through all the characters.

#HomebrewComputer #Electronics

The MC6847 in the test rig, but now the jumpers permanently pulling the 8 databits of the device to ground has been replaced with Dupont wires connected to the lower bits of the address bus of the device.

The monitor now, repeatedly, showing all of the 64 characters of the built in charset, instead of just the @ sign.

Time to hook the stages up... And it works! 😅

Going for broke, I didn't bother to impedance match or AC couple, hooking the small TV's composite port directly to the output of the amplifier stage, hooked up to the Y output of the #MC6847 I received from @ometeer

This awesome monochrome 32x16 screenful of @ signs is the first milestone of adding video to my SBC#0 project. 🤓

#HomebrewComputer #Electronics

The MC6847 test rig, connected up to a breadboard with the inverting amplifier stage.

On the left, a stack of test equipment. On the wall, a small wall mounted TV in composite mode, hooked up to the output of the amplifier on the breadboard, is showing a regular pattern of characters.

A scope connected to the output of the amplifier stage shows a composite video signature, now with the right polarity.

A close up of the monitor. The screen is full af @ signs, corresponding to the hardcoded 0 at the MC6847's databus. There are 32 colums and 16 rows.

Need to fiddle a little with the output signal level (plus I should load it with 75Ω like a TV would) to be on spec, but something like this should be good enough for a #MC6847 test video driver.

(It's a common emitter amplifier, inverting the signal from the VDG, followed by an emitter follower for buffering.)

#electronics

A breadboard with 2 transistors and a handful of resistors. A probe from a signal generator and 2 probes to a scope is hooked up to it.

A hand sketched schematic on a postit note is in th background.

A signal generator set up to produce a sine wave between 0 and 1V at 100 KHz.

A scope showing 2 traces: the original signal from the signal generator and an inverted signal, about twice as large and with a DC offset from the breadboard output.

Testing the #MC6847 received from @ometeer

Just reviewing the expected signal outputs at this stage. Need to do a little inverting signal amplifier before being able to drive an actual composite video input. That'll be the next step if all is good.

An MC6847 sitting in a test rig on a messy work bench. A signal generator and scope probe is connected to it. It the background is a power supply.

A signal generator set up to produce a 0V/5V square wave output at 3.579545 MHz.

The #MC6847 graciously donated by @ometeer arrived over Christmas. 📦 Hope it made the journey safely, hope to find a window to sanity check it in the test rig later tonight. 🤓

Second attempt to source some #MC6847 ICs for my #homebrewcomputer.

Previous ones didn't behave as expected in the test rig, maybe these will...

#electronics

A couple of MC6847P video display generator ICs, recently unpacked from a pink antistatic bag.

In the background is a breadboard with a simple test rig for the VDG.

Oh yeah, and what are you gonna *do* about it?

#homebrewcomputer #mc6847 #electronics

#MC6847

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