TU58 tape formatter (was Re: rebuilding DC100A cartridges?)

[Ethan Dicks]

On Sat, Nov 24, 2012 at 4:08 AM Eric Smith <eric at brouhaha.com> wrote:
> I spent some time reverse-engineering the firmware.  There is only one
> undocumented opcode, decimal 10, and I haven't yet figured out what it
> does, but it definitely doesn't format a tape.

I looked at the firmware disassemblies.  Opcode 10 appears to only
point to code (vs NOP) on one version of the firmware

https://gitlab.com/NF6X_Retrocomputing/tu58firmware/blob/master/disassembly/23-089e2.asm

op_undoc_10:
    ld    hl,l07e4
    call    s06a
    ld    a,018h
    ld    (r2003),a
    jp    op_nop

(I think the jump to op_nop is just there to handle regular opcode
processing cleanup)

I have TU58 drives in VAXen (11/750, 11/730, 11/725), a VT103, and one
standalone unit that I pulled from an 11/725 that we bought to strip
for parts to keep our 11/730 running.  I really haven't explored the
differences in the firmware since mostly, I've used them as intended,
for loading SA Backup, Microcode patches, and, of course, as Console
Media to boot the 730 and 725.

-ethan