NewRisingSun
Member
- Joined
- May 21, 2013
- Messages
- 46
I have dug deeper into the Tandy 1000's "Extended Addressing Mode" and noticed that the Tandys with the "Big Blue" video chip (EX, SX, HX, TX) also support interlaced true scanning. (The original IBM CGA aligned the synchronization signals always so that scanning would be progressive no matter the CRT controller's setting. I don't know if this is also true for the PCjr and original Tandy 1000.) Together with the 2x32K banks per page feature in the Extended Addressing Mode, this enabled me to create true 320x400x16 and 640x400x4 video modes on the TX. They look quite nice, if one is willing to accept the flicker and, for 640x400 mode, the four color limitation.
It would be great if someone could try this on an RL, SL or TL. The TL reference manual lists CRT controller register 8, which normally is the interlace register, as "Reserved", so it may be that Tandy removed the interlace mode from the "Tandy Video II" chip, which would be quite unfortunate.
These are two images: one with 640x400 text (8x16, from VGA), and one showing the Pinball Fantasies title screen (reduced to four colors). As with the modified IntroJR, this will not work on the original Tandy 1000/A/HD since they do not have the Extended Addressing Mode.
It would be great if someone could try this on an RL, SL or TL. The TL reference manual lists CRT controller register 8, which normally is the interlace register, as "Reserved", so it may be that Tandy removed the interlace mode from the "Tandy Video II" chip, which would be quite unfortunate.
These are two images: one with 640x400 text (8x16, from VGA), and one showing the Pinball Fantasies title screen (reduced to four colors). As with the modified IntroJR, this will not work on the original Tandy 1000/A/HD since they do not have the Extended Addressing Mode.
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