Here are my SBC-2 Operating System Source Files.

They include:

sbc.asm   - The build file that includes all the other files in the proper order
            (you would assemble this file with TASS)

reset.asm - reset and IRQ initialization
sbcos.asm - monitor & minassembler
acia.asm - 65c51 init and IO support for monitor
via1.asm - via # 1 init
via2.asm - via # 2 init
basic209.asm - Enhanced Basic 2.09 (modified slightly from Lee's distribution)
basldsv.asm - load and save routines for EHBASIC.
upload.asm - XMODEM/CRC & Intel-Hex File Upload support

Compiled using TASS using the following command line:
TASS /c /lsbc.lbl sbc.asm sbc.bin sbcos.lst

The compiler list output file from TASS is called:
sbc25.lst

The label file contains all the labels and their addresses and is called:
sbc.lbl

There are 2 compiled files included:
sbc25.rom  -  the 32k raw binary object file (only the upper 20k are used)
sbc25.hex  -  the Intel HEx formatted 32k file.

I've enclosed a binary to intel-Hex conversion file if you need to use it:
bin2hex.exe

Good luck!

Daryl