Great Hierophant
Veteran Member
I cannot seem to find any homebrew memory board upgrades for the Tandy 1000 EX or HX that include the DMA function. DMA is typically required for DRAM refresh, but SRAM does not need periodic refresh and all homebrew upgrades use SRAM. DMA is also typically used for floppy disk drive data transfer, but if the floppy drive is reading or writing, you are pretty much waiting until it finishes, DMA or no DMA. DMA is also used by things like a Sound Blaster and an ECP parallel port, but try getting one of those things to fit inside the cavity for the PLUS cards in the EX and HX!
Anyway, there is one benefit to DMA that I feel is important, and that is compatibility with floppy disk protection. There are several games with protection schemes that will refuse to work if they do not see a DMA controller in a "PC", which is what a Tandy identifies as to non-Tandy aware software. (A few do work on a PCjr, which has no DMA, because the protection has a DMA-less exception for that system). They include :
Crossfire (PC) (Not PCjr. compatible)
Crossfire (PCjr rev1)
Frogger (Not PCjr. compatible)
GATO (v1.4)
The Great Escape (Thunder Mountain)
Hardball (Accolade) [5.25 rev0] (EGA Disk)
Hardball (Accolade) [5.25 rev1] (EGA Disk)
Hardball (Tandy Corp.)
King's Quest (128k Sierra PC rev0)
King's Quest (128k Sierra PC rev1)
Mr. Cool (rev0)
Quink (Thunder Mountain)
Top Gun (Thunder Mountain rev0)
Ultima II (Sierra PC rev0)
Ultima II (Sierra PCjr)
Ultima III (rev0)
Ultima III (rev1)
Ultima III (rev2)
Ulysses and the Golden Fleece (Not PCjr. compatible)
This video shows an ISA card solution, but I can see no reason why it could not be adapter to the PLUS form factor or attached to a PLUS adapter to add DMA to the EX or HX :
(links to github in video's description) Anyone have any experience with this?
Anyway, there is one benefit to DMA that I feel is important, and that is compatibility with floppy disk protection. There are several games with protection schemes that will refuse to work if they do not see a DMA controller in a "PC", which is what a Tandy identifies as to non-Tandy aware software. (A few do work on a PCjr, which has no DMA, because the protection has a DMA-less exception for that system). They include :
Crossfire (PC) (Not PCjr. compatible)
Crossfire (PCjr rev1)
Frogger (Not PCjr. compatible)
GATO (v1.4)
The Great Escape (Thunder Mountain)
Hardball (Accolade) [5.25 rev0] (EGA Disk)
Hardball (Accolade) [5.25 rev1] (EGA Disk)
Hardball (Tandy Corp.)
King's Quest (128k Sierra PC rev0)
King's Quest (128k Sierra PC rev1)
Mr. Cool (rev0)
Quink (Thunder Mountain)
Top Gun (Thunder Mountain rev0)
Ultima II (Sierra PC rev0)
Ultima II (Sierra PCjr)
Ultima III (rev0)
Ultima III (rev1)
Ultima III (rev2)
Ulysses and the Golden Fleece (Not PCjr. compatible)
This video shows an ISA card solution, but I can see no reason why it could not be adapter to the PLUS form factor or attached to a PLUS adapter to add DMA to the EX or HX :