Tandy13h is an experimental VGA/MCGA mode 13h emulation TSR driver for the Tandy Video II adapter that can be found in the Tandy 1000 RL, SL and TL series of computers.
The TSR driver can be loaded via
TANDY13H.COM
It can be unloaded via
TANDY13H.COM /U
Once the driver has been loaded, programs can switch to mode 13h as if they were running on a system equipped with an MCGA or VGA card.
This driver maps the 256 color mode of VGA and MCGA cards with its 320x200 pixels to the Tandy Video II adapter's 16 color mode with 640x200 pixels. Both those modes use segment A000h as frame buffer and share practically the same memory model. Every 256 color pixel will show up as a pair of 16 color pixels.
The output on-screen will look similar to a 256 color picture with a palette that consists of the average colors of all possible pairs of CGA colors, albeit with vertical stripes. This implicit palette cannot be changed. Furthermore, any functionality that bypasses the video BIOS cannot be reproduced.