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I'm adding the external character generator to the Dragon 200-E in MAME but the INT/EXT line on the 6847 is never being asserted. It's hooked up to PIA1 Port B bit 4, same as GM0, but is never set to enable use of the external ROM. Also looked at the vdg_fetch_handler_chargen in XROAR but also seems to suggest I should be seeing INT/EXT being set. Are there any other hardware differences I need to consider or should I expect pressing SHIFT+SPACE to set INT/EXT?

Hi,

The internal/external character switch is done by poking values to 0xFF22.

If you need to test something on the real machine I can ask the guy who actually owns it.

Cheers,
Rob

robcfg wrote:The internal/external character switch is done by poking values to 0xFF22.

It makes sense that $FF22 is poked as this is PIA1 Port B, but I'm only seeing 0x04 being written during key presses. I'd expect 0x10 to select the EXT ROM.

I wonder whether I need to do something with link LK1 to indicate that the external chargen is available?

LK1 switches between standard and inverse video.

The INT/EXT signal goes directly to A7 on the eprom, the INV signal from the motherboard goes to one input of the 74LS00 and the output from that nand goes to the 6847 INT/EXT pin.

What I think it happens is that, when a non inverse video character is requested, the 6847 switches to the external ROM. When an inverse video character is requested, the standard characters are used. The characters appear normal or inverse, depending on the LK1 switch.

I made a composite view of the daughter board, and also some annotations.

Please check the attached pictures.

Cheers,
Rob

I'm almost there with this, but struggling with the semi-graphic colours. Any ideas as to what I'm missing here?

This is what you should be seeing if you write the following program:
As far as I know, the semigraphic characters are automatically generated by the VDG and are not stored anywhere, so you may have an addressing issue there.

In sg4 IIRC d7 also goes to the a/s pin on the vdg, and then bits 0..3 select one of 16 patterns. Bits 4..6 select 1 0f 8 colours. So I suspect if d7 is high and a/g islow all 8 bits need togo to the vdg.

Cheers.

Phill.

We're any of these additional characters actually typeable on the keyboard, such as the lowercase?

You can try it in XRoar - a few are typeable.

Acute accented characters are typed with apostrophe followed by the letter (caps lock must be off - Shift+Enter).

Shift+0 for ç

Shift+Break for ü

Right for ï, Shift+Right for ¿

Down for ã, Shift+Down for ¡

ñ/Ñ have a key dedicated to them.

Shift+Space for §

And because there's no @ key on the D200-E keyboard, Shift+Clear for @

Those are all the ones I know about...

sixxie wrote:Acute accented characters are typed with apostrophe followed by the letter (caps lock must be off - Shift+Enter).

Thanks, having never actually used a Dragon I wasn't aware of SHIFT+ENTER.