DEC Professional 380, TMS and EBO questions

Paul Koning paulkoning at
Tue Apr 12 09:30:47 CDT 2016

> On Apr 12, 2016, at 9:57 AM, Pontus Pihlgren <pontus at Update.UU.SE> wrote:
> On Tue, Apr 12, 2016 at 09:32:43AM -0400, Paul Koning wrote:
>> No.  You can find all this in the Pro300 series technical manual, on 
>> Bitsavers.  The base video module is one plane, so black/white only.  
>> The EBO module adds two more planes.
> One technical manual(EK-PC350-TM) on bitsavers is for the 350 only. 
> Which states that you can sacrifice resolution for more shades.
> The other (EK-PC300-V1 and -V2) covers both the 350 and 380 but is less 
> than crystal clear when it comes to the Bit Map Video Controller on the 
> 380.
> I'd be surprised if the 380 behaves differently, but I wanted to know if 
> anyone knew for certain. I read somewhere that few programs used the 
> lower resolution so in practice it might not matter so much.

I only have a base video 380 (and, perhaps, parts of others that I haven't really analyzed).  So my coding has only been for that base functionality.

The 380 design matches that of the 350 functionally, for the parts that were considered relevant.  For example, the misguided parts of the original Intel interrupt controllers don't exist in the 380 interrupt control logic, but the parts that are used by Pro software are unchanged in both.  Similarly, as far as I remember, the video logic is compatible between the two.  In the 380, video is built-in and appears in "slot 6" (the address block after the highest real I/O card slot, number 5).  The 380 video is described in chapter 6, but given the compatibility, if you want more detail you can use the 350 video documentation as needed.  If there is a conflict, assume the 380 documentation gives the right answer, but if the 380 section leaves something out, you can assume the 350 analog is the answer for both.

Ok, so in looking more closely, I see a register that lets me chose 1024 bit resolution B/W, 512 bit resolution in 4 levels of gray, 256 bit in 16 levels.  I haven't used that.  (Instead, I used every other pixel for normal intensity, set all pixels for bold -- for 80 column text.  For 132 column text there aren't enough pixels for that so I didn't support bold there.)  It seems that this variable resolution stuff is valid even without EBO, but if you do have an EBO it applies only if you have the colormap disabled.  With the colormap enabled, you have 8 colormap entries indexed by the three planes, and you get 4 bits of intensity per channel.  (This is a place where the Pro 350 is different, it has only 3 bits per channel.)


More information about the cctalk mailing list