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Wondering what the 20 pinout holes was used for. It is below the speaker on the keyboard, has a further four pinouts above, and has something to do with the cartridge system in later models, I guess.

Are there any mods available?

Have found this item http://chrisacorns.computinghistory.org.uk/8bit_Upgrades/Viglen_BBCCart.html, but it doesn't fit into the pins as such, and instead connects into a rom slot via cable connector.

And this also does a similar job http://chrisacorns.computinghistory.org.uk/New4Old/RetroClinic_Beebzif.html

Space for a small Zif port perhaps?

Am interested about the original use of these pinouts

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    Welcome to Retrocomputing Stack Exchange. Please read the tour. It's good to see that you did some research before asking the question; hopefully that will set somebody on the right path. – wizzwizz4 Jan 27 '18 at 15:17
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Most hobbyists put a ZIF socket onto those pins. This then was connected through to the sideways ROM sockets on the motherboard.

The socket enabled you to insert language ROMs as required, thus not using all the available sideways sockets.

However, the main purpose was to fit the Speech Synthesizer unit.

Fitting this required modifying both the main PCB and the keyboard PCB. It was not for the faint hearted but gave a remarkably high quality speech for its time.

The speech being generated by requesting individual phonemes from the Synthesizer in sequence. The speech being the digitised voice of Kenneth Kendall.

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    The main PCB has a slot for both the TMS5220 speech engine, and a TMS6100 phoneme ROM. The speech upgrade involved fitting these chips to the motherboard - the keyboard wasn't modified. The 'ashtray' slot was for fitting additional phoneme ROMs, literally in parallel with the first. The TMS6100 is a mask ROM and used in other products, so there were different versions about - but others weren't widely used on the BBC Micro. – user1908704 Jan 27 '18 at 22:12
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The “ashtray” was supposedly meant for serial PROM cartridges, but was often modded for other purposes. Cartridges were becoming rarer by the time the BBC Micro was released, though, and regular EPROMs became the medium of choice.

ISTR the Acorn Speech Synthesizer used some hardware in or around that slot.

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The phroms don't have to be phoenim based. You can see this in AstroBlaster which doesn't even use a phrom or in the Star wars demo that plays back the speech from the arcade game which used the same tms5220.

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