Monday, December 7, 2020

The Tandy 1000 Saga: catching up.

I'm bad at blogging.

There, just got that out of the way.

Since I last updated this blog over a year ago I've uploaded a few more YouTube videos on the subject of the memory board project I initially started a few months after getting a bare Tandy 1000 EX in the middle of 2019. A lot has happened since then. Here's the latest video, in which I'm demonstrating the capabilities of my latest and perhaps ultimate variation of a Tandy 1000 EX/HX expansion board:

Here is a link to a playlist of the previous videos.

In short, the current version of the board, which is implemented using a couple of GAL (Generic Array Logic) chips in order to fit everything (tightly) into the space available while retaining the use of through-hole parts for easy assembly, includes the following features:

  • Expands base memory of a bare 1000 EX/HX to 640K
  • A "spare" 128k is available to be mapped into the upper memory space between C0000 and EFFFF, with several switch-selectable options to optimize utilization.
  • Two additional sockets for 512k SRAMs are available and can be populated to provide 1MB of EMS memory. Page frame location is adjustable.
  • 44 pin laptop PATA connector to be used with either a CF or SD adapter to provide hard disk storage via a single-chip XT-CF-Lite implementation.
  • In-system programmable Flash ROM for the XTIDE BIOS, location is switch adjustable.
  • Dallas 1215/1315 "zero-slot" clock compatible with Radio Shack's original "Smartwatch" option.
  • Dual 9-pin 16550-compatible serial ports; switch settings allow one to use a nonstandard IRQ to free up IRQ 3 for other expansion cards while working as a dedicated mouse port in conjunction with the CuteMouse driver.
  • Expansion passthroughs compatible with the original Radio Shack cards; can be used with genuine Plus cards or with an ISA adapter for network or VGA cards.
  • With the latest GAL programming and the aid of a jumper wire can override the built-in DOS-in-ROM in the Tandy 1000 HX, freeing up memory space for use as UMB or EMS page frame. Also allows relocation of XTIDE BIOS to F0000, which is very useful if an option card that has a ROM (like a VGA card) is installed.

Anyway. This board is currently not for sale; I don't think I have the bandwidth in my life to produce it, alas. But it's been an interesting project, and very educational.

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