Classic Systems, Contemporary Gear
With the introduction of the TANDY Color Computer (CoCo) 3, engineers were faced with 2 significant and implied mutually exclusive goals: To satisfy both of these goals, the CoCo 3 consolidated the MC6883/74LS783 Synchronous Address Multiplexer (SAM) and the MC6847 Video Display Generator (VDG) into a single Application Specific integrated Circuit (ASIC) while adding additional Continue reading…
As noted in a previous post, along with finding that Green Mountain Micro (GMM) had created a lowercase modification for the CoCo called lowerkit , Eurohard SA also created a lowercase update for the Dragon 200e for the Spanish market, which I think was planned or actually produced as an official part of the Dragon 200e Continue reading Expanding the MC6847: Deciphering the Interface, Part 2
Another Player Enters the Game While searching for TANDY Color Computer external font solutions, I found information on a similar solution that was created for the Dragon 200e. As a TANO Dragon owner (basically, an imported Dragon Data Dragon 64), I was aware of the Dragon line, but the 200 (and 200e) were new to Continue reading Expanding the MC6847: Deciphering Fonts, Part 2
Having found some external fonts used with a MC6847 lowercase modification from back in the day (the lowerkit product from Green Mountain Micro) and converting them into ROM-burnable images, I determined a ROM font was composed of 12 bytes of font bitmap data, with 4 bytes of padding to align font data on 16 byte Continue reading Expanding the MC6847: Deciphering the Interface
Searching for Information As I was trying to decipher how to leverage an external character font ROM with the MC6847, I searched for existing project/products in this space. My web searches first found Ed Snider s (Zippster of ZippsterZone) reproduction of the Green Mountain Micro (GMM) lowerkit product from back in the day . Ed shared a Continue reading Expanding the MC6847: Deciphering Fonts
Understanding external character ROM functionality on the Motorola MC6847 Video Display Generator (VDG) I ll be honest, I rarely use lowercase characters on any of the classic computers I use. Back in the day, of course, I needed them when writing posts on BBS systems, composing school papers, and writing general correspondence (my handwriting was never Continue reading How Low Can You Go?
Addressing the Color Computer 3 DMA operation challenges via hardware modification, while pretty simple, limits initial adoption. It places the technique into a classic “chicken and egg” situation. The CoCo3 provides an ideal platform for DMA capabilities, but owners will only perform hardware modification if highly desired peripheral capability demands it. Hardware designers, for their Continue…
Radio Shack’s introduction of the Color Computer 3 introduced extensive changes to the Color Computer design. Gone were the 6847 VDG and 6883 SAM, functionally replaced and enhanced with the TCC1014 Advanced Color Video Chip (ACVC) which most folks reference as the GIME. Other additions included an additional 64kB of RAM with an option to Continue reading CoCo DMA: Missing Without a Trace
Now that we’ve learned a bit about how the 6809E wants to be treated during a direct memory access (DMA) request, we can put all we’ve learned into action. But, before we launch into the details, let’s address some questions that arose during previous article discussions: Some asked why the logic doesn’t just watch for Continue reading CoCo DMA: Invisible RAM
Picking up from last time, we were able to successfully place a byte into the internal CoCo memory from the cartridge port without the use of the CPU by utilizing a direct memory transfer procedure. However, after the transfer, BASIC programs would stop with errors at times, machine language programs would simply lock up, and Continue reading CoCo DMA: “Fighting on the bus”