Subj : Re: Commodore history - The Commodore 128 by The 8-Bit Guy
To   : All
From : Martijn van Buul
Date : Fri Oct 19 2018 08:51 am

* Andreas Kohlbach:
> On 17 Oct 2018 21:05:34 GMT, Etienne von Wettingfeld wrote:

>> The C128 indeed has a Z80, for CP/M mode. In fact, the computer boots using
>> the Z80.
>
> Are you sure?

I'm quite sure Etienne is - and so am I ;)

>> It has an Assembler monitor, but I think Lucifer means two screens at once.
>>
>> It actually can, one using the 40 collumn mode and one the 80 character one.
>
> But not at the same time AFAIK. When you switch the mode the content what
> was displayed in the mode before just froze on the other display.

Well, that depends on your point of view. There are a few gotchas:

The 40 column screen used a video chip closely related to the one in the
C64. As such, it could only operate on 1MHz - if you wanted to use the
128's higher clockspeed (a blazing fast 2MHz), you were forced to blank
the 40 colum screen and use the 80 column screen instead (as it used a
separate video chip which didn't have this limitation).

So it did make sense to disable the 40 column screen, if the user switched
over to 80. This is assuming that the user didn't really have 2 monitors
to begin with, but only switched input source on their monitor - the 40
column output would go to waste anyway.

But that doesn't mean it couldn't be done to have both outputs active. In
fact, it was quite normal for software development.

A random demo I found on the interwebs:

https://www.youtube.com/watch?v=s2dcqkM-jeM


--
Martijn van Buul - pino@dohd.org
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