TRS-80 Model 1 Notes
DH is unable to support the TRS-80 Model 1 system for a couple of reasons.
The main reason is that “out of the box” the TRS-80 was limited to 16KB. While a RAM expansion board was eventually available, it is unclear how the modern C compiler references that hardware. In any case, the intent for DH was to target original “out of the box” systems. [ it may be possible to load DH into the RAM expansion board of the TRS-80 Model 1 and invoke execution there; but emulators do not support this configuration and so it is difficult to verify without actual hardware ]
Another issue is the Model 1 uses a substantially different character set than the Model 3, so a single binary to support both the Model 1 and Model 3 would not be practical (doing so would increase the code-size of the program).
One additional reason for less emphasis on supporting the Model 1: The TRS-80 Model 1 was never fully FCC approved, due to lack of shielding and RF interference issues. The Model 1 was discontinued in January 1981 due to these issues, replaced by the Model 3 sales. Further details are here.
For reference, the Commodore PET was discontinued a year later in 1982 (with sales replaced by the VIC20 and Commodore 64). The original Apple ][ was also discontinued in 1981, with the Apple ][+ discontinued in 1982 (both replaced with Apple ][ e and other Apple models). The IBM PC released in August 1981 essentially marked the end of the 1977-1981 era of “power up BASIC” Personal Computers, and entered the new era of DOS (Disk Operating System). [systems with ROM BASIC were still sold for about another decade, till about 1991, for education and casual usage – but DOS systems and high level languages like C, Pascal, Fortran increasingly dominated the commercial software market]