[HN Gopher] The Character Generator ROM
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       The Character Generator ROM
        
       Author : alraj
       Score  : 30 points
       Date   : 2023-08-11 06:22 UTC (1 days ago)
        
 (HTM) web link (www.atariarchives.org)
 (TXT) w3m dump (www.atariarchives.org)
        
       | JdeBP wrote:
       | Some of those block diagrams were a bit oversimplified. One
       | cannot address 9 rows with only 3 address lines, for example. Or
       | do block graphics with just 4 NOR gates.
        
       | jandrese wrote:
       | I think there is a typo in the first graphic on that page, on the
       | top row the second column is labeled 0011 when it should be 0001.
        
         | sedatk wrote:
         | A 44-year old typo, to be exact. :)
        
       | chrisco255 wrote:
       | (1979)
        
       | rbanffy wrote:
       | Oh... That's just the start of the trickery. DEC and HP (and the
       | Apple II, in high-res mode) had tricks to shift (delay, really)
       | groups of pixels by half a pixel, giving us better A's and V's,
       | and more rounded O's.
        
         | raphlinus wrote:
         | So the HP 2645 _did_ use a half-bit shift and it 's quite
         | clever. It's shown in this video[1] by CuriousMarc (I've set
         | the timestamp to the relevant part). The document shown in the
         | video is available on the Internet Archive[2]. It also reminds
         | me of techniques used in Epson dot matrix printer fonts, where
         | the _rate_ of pin firing couldn 't be increased, but the half-
         | pixel timing could be.
         | 
         | I'm pretty sure DEC VT100 and VT220 did not do this. There _is_
         | some dot-stretching logic in the VT100 and VT220[3], which
         | improves appearance but doesn 't increase effective resolution.
         | 
         | Apple ][ is a slightly different story. The high bit (very
         | similar to the HP terminal) does cause a half-pixel shift, but
         | I believe this was almost entirely used to create more colors
         | through NTSC artifacts, not to increase horizontal resolution.
         | I'm unaware of a character ROM that uses the technique, but I
         | could be missing something. The best writeup I've found is [4].
         | 
         | [1]: https://www.youtube.com/watch?v=QikO0WOAGWI&t=371s
         | 
         | [2]:
         | https://archive.org/details/bitsavers_hpterminaleriesCharact...
         | 
         | [3]: https://www.masswerk.at/nowgobang/2019/dec-crt-typography
         | 
         | [4]:
         | https://retrocomputing.stackexchange.com/questions/6271/what...
        
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       (page generated 2023-08-12 23:01 UTC)