Date : Tue, 18 Dec 2001 14:57:44 +0100
From : cbrashol@...
Subject: Re: International fonts & mode 7
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Hi all,
I have a beeb with a scandinavian (probably swedish) mode7 chip install
ed, and
have seen quite a few others here in Denmark.
Some of them also has a modified OS -ROM, with a sligthly different key
board
mapping, and danish characters coded in indstead of [|] {\}
Regards
Carsten Langkvist Brasholt
HR- & Competence Manager
Training and Consulting
CSC Consulting Group holder lukket den 27. og 28. december.
Vores Kundeservice har =E5ben 8.30 - 16.30 begge dage og vil s=F8rge fo
r
viderestilling til de personer med tilkaldevagt.
CSC Consulting Group A/S
Herlev Hovedgade 199
DK-2730 Herlev
Tlf: +45 3614 5200
Direkte: +45 3614 5313
Mobil: +45 2923 5313
Fax: +45 3614 5395
www: www.csc-training.dk
Mail: cbrashol@...
|--------+----------------------->
| | "Richard |
| | Gellman" |
| | <r.gellman |
| | @btinternet.c|
| | om> |
| | |
| | 14-12-2001 |
| | 14:27 |
| | |
|--------+----------------------->
>-------------------------------------------------------------------|
| |
| To: "BBC Micro Mailing List" <bbc-micro@... > |
| cc: |
| Subject: RE: [BBC-Micro] International fonts & mode 7 |
>-------------------------------------------------------------------|
--0__=iGDe2xaXbAcbDFGdfOmZl8Go4N7dkr3i8rr1JgF4mh4lMxfciDVJZtEV
First of all, the definitive on Mode 7/SAA505X
>From the datasheet no less...
There are no registers on the SAA5050 that can be programmed. Only its
internal counters, etc.
The Chip numbers are as follows:
Chip Character Set
5050 English
5051 German
5052 Swedish
5053 Italian
5054 Belgian
5055 US ASCII
5056 Hebrew
5057 Cyrillic
As far as I can tell, the foreign chips just had different symbols used in
the normal character range 32-127.
The resolution was internally fixed at 6 pixels by 10 pixels for
alphanumeric characters.
All processed character codes were 7-bit (0-127), codes 128-255 being
duplicates of 0-127.
The graphics characters were "2" by "3" "blocks". each block is 3 pixels
wide, the top and
bottom block rows are 3 pixels high, and the middle row blocks are 4 pixels
high 3+3+4=10.
In separated graphics mode, the bottom row and right hand column of pixels
in each block is
set to background colour.
The resolution is doubled both horizontally and vertically by the use of
character rounding dots.
These dots are NOT hard coded into the chip, and are added at display time
by a diagonal detection
circuit which detected two pixels in a "2 on a dice" arrangement, and
inserted the "half-pixels"
in between them. In double height mode, the half pixels were not doubled in
height. This effectively
increases the resolution to 12x20.
On the 6x10 grid, the right-most pixel and bottom-most pixel in alphanumeric
mode are set to the
current background colour, to space out the characters, giving a used
alphanumeric resolution of 5x9
(no alphanumeric pixels went outside of this grid).
Character rounding can be disabled by deasserting the CRS pin. (which is
tied asserted on the bbc micros).
The bbc micro displays these extra half pixels by switching to interlace and
sync mode, which doubles
the visible vertical resolution, causing the bbc-micro's mode7 outputted
resolution to be 480x500.
This is not a 4:3 ratio as per the 1280x1024 (os-pixels) resolution of modes
0-5 (not 3). And causes
the mode 7 screen to appear horizontally squashed (like a widescreen picture
on its side).
The trick discussed previously on this list which effectively disabled the
character rounding worked
by switching back to video mode, and adjusting the lines per character
register so that the half-pixel
lines were effectively ignored.
All of this is fully supported (except the foreign chips) in BeebEm 1.4 :)
Joel Rowbottom wrote:
>Mind, it would be nice to be able to tie an emulator serial port to a
>socket, so that I could log into ccl4 on an emulator...
I have in mind a BeebEm plugin (post 1.4) that will connect the serial port
to an address via telnet.
Enjoy :)
-- Richard Gellman
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