home *** CD-ROM | disk | FTP | other *** search
- From: bdb@cl.cam.ac.uk (Brian Brunswick)
- Subject: High res mono mode 23 with Taxan 795
- Date: 29 Jan 91 19:24:19 GMT
-
- While messing about one day, I happened to try Mode 23 from my A440 on
- my Taxan 795 monitor, (by typing *CONFIGURE MONITORTYPE 2, which makes
- all modes into 23) and it successfully synced to it. However, the
- result appeared very strange, since I was still using the normal
- monitor lead. (This is because the high resolution mono mode relies
- on a special serialisation circuit which converts one 16 colour pixel
- into 4 adjacent black and white pixels by splitting out the bits, and
- this output only goes to the 2 BNC connectors on a 400 series, not the
- normal video connector.) I determined to make up a lead to get a
- proper view of this mode, and I will detail here how this was
- eventually done.
-
- The first problem was obtaining a 15 pin (three row) D-type connector
- (male) to plug into the 795, which took several weeks because it was a
- strange thing, and therefore out of stock. Eventually, this arrived,
- and I tried making a lead, working from the rather sparse information
- in the 795 manual, which gave only a pin out diagram for the
- D-connector, and no explanation at all. From past experience, I
- distrusted trying to make up BNC plugs, so I used some BNC to phono
- connectors, and some phono plugs, and also some two core separately
- shielded cable that I had around. What I made at first didn't work,
- but by circuit testing the standard lead, I eventually found that the
- secret was to feed composite sync only to the hsync input of the 795,
- and leave the vsync unconnected. Naturally, there was no mention of
- this in the 795 manual.
-
- So what I had then, was a fairly blurry picture, on which it was not
- really possible to even distinguish the background pattern, which has
- a 4x4 pixel cross hatch.
-
- Wiggling wires soon discovered that it was the phono plugs at fault,
- and so I then did what I should have at the start, which was to get a
- ready made BNC to BNC lead, and cut it in half. The resulting lead,
- with the D-connector in a shielding metal case, and stuffed two or
- three times through an old ferrite core that I had lying around
- produces quite an adequately sharp picture. Individual pixels are not
- quite visible, but this is understandable considering it is exceeding
- the 795's 50Mhz pixel rate with 64Mhz, and its stated resolution of
- 1024x768.
-
- Now personally, I don't think I will actually be using mode 23 much.
- Its resolution is only 1152x896 in 2 colours, and quite frankly I
- prefer the VIDC enhanced 1152x448 in 16 colour mode that is
- obtainable, with the same apparant wimp scale. But this may well be
- useful to those needing to test stuff in all modes, or emulate X
- windows, or whatever. What is really needed is a switch over method,
- but I doubt that can be built sufficiently cleanly.
-
- Anyway, the details of connection are as follows:
-
- 15 pin D-type connector, looking into monitor, or back of plug
- -----------------------------------------
- \ id |
- | GND gnd B G R /
- \ 5 4 3 2 1 /
- | +---+---+---- connect all 3 to core of signal BNC lead
- \ /
- | KEY corresp ground returns
- \ 10 9 8 7 6 /
- | + +---+---+---- connect all 3 to ground of singal BNC lead
- ground of sync BNC lead |
- \ syncs Id /
- | NC v h NC GND |
- \ 15 14 13 12 11 /
- | + |
- core of sync BNC lead /
- --------------------------
-
- If anybody tries this, I'd be entertained to hear from you how useful you
- found it.
- Brian.Brunswick@uk.ac.cam.cl Disclaimer. Short sig rules!
-