On 12/16/20 5:57 PM, Scott McDonnell wrote:
I am actually more excited that I have the custom carriers for the
option ROMs than the ROMs themselves. Ultimately I am looking to build
my own custom option ROM as I have an end use for this in mind that will
give it a relatively single purpose.
The carrier won't do you too much good most likely.
The socket has a non-standard pinout, and so most roms and definitely
any chip you can write (27C256), needs a pinout adapter as well as a way
to make the physical connection.
You could make use of the adapter if one of these is true:
* You have a DIP-28 (or larger) test clip AND the pinout adapter doesn't
hard short the VPP pin to VCC or GND. I think they all do. If it had a
10k+ resistor instead of a trace, then it would be ok, but no commercial
rom maker did that that I ever saw. If the adapter hard-shorts vpp, then
you need to desolder the chip from the adapter to write it, or at least
cut the vpp leg and add a resistor and removable jumper to the adapter
somehow.
* Or unless one of your adapters is a "ROMBO", like this:
https://goo.gl/photos/AaqKUGoY6oGEZdxM6
Otherwise I expect the Disk+ one at least, if not both, is the same as this:
https://photos.app.goo.gl/SN7qC3BXXBFX7bMg7
There is another style like this:
https://photos.app.goo.gl/zRyssWsAuXTAWHwV6
And finally there is the Multiplan style where Tandy actually had custom
chips made that had the right pinout, so they are just installed in the
Molex carrier normally. But those chips are special. You can't do that
with a 27C256.
Otherwise in all cases except the ROMBO, the chip legs are either bent
around the standard carrier or soldered into a pinout adapter pcb.
Either way it makes it a problem to write the rom more than once. Even
for the style that doesn't need soldering, you can't bend and unbend the
legs very many times before one breaks.
If you have a rombo style, then the 27C256 can be installed and removed
and reinstalled in the adapter as many times as you want without bending
the legs, so you can remove the chip from the pinout adapter to re-write
the chip all you want.
You're going to want to get a REX#, REXCPM, REX Classic, or make a
Teeprom, if you want to play with writing and hacking on roms.
REX is like a software controllable, software loadable, on-board option
rom library. REXCPM is that plus the amazing ability to replace the
normal system rom with CPM and up to 4M of virtual disk. (all purely in
ram though so it's kind of touchy vs REX Classic or REX# which are flash
based)
REX# or REX Classic would be the hands-down most convenient way to play
with roms. You load them as ordinary files from a modern pc over the
serial port, and load up to 32 of the and overwrite them all you want.
No burner, no uv eraser.
Teeprom needs a burner and a soic-28 test clip, but at least no uv
eraser because the rom chip is 28C256 instead of 27C256. It DOES have a
resistor instead of a dead short for vpp so it can be simply connected
to the a burner and written at will. There are a few odd cases where you
want a plain rom and not a REX, but honestly not many.
REXCPM , REX#
http://bitchin100.com/wiki/index.php?title=Rex
REX Classic (buy)
https://www.arcadeshopper.com/wp/store/#!/REX-with-holder/p/177952983/category=28313042
REX Classic (build your own)
http://tandy.wiki/Building_a_REX
Also, for REX Classic, this board provides a good way to use the
software main rom feature that only REX Classic has:
It provides a main rom on a updateable 28C256, so you could install a
y2k-patched version, but the real point is it provides a convenient way
to hook up the /CE line for REX to take over the job of providing the
main rom, but also let's you remove the REX and re-enable the internal
rom without taking the machine apart again.
http://tandy.wiki/FlexROM_100
And for a plain rom:
http://tandy.wiki/Teeprom
If you still wanted some of the carriers knowing about the pinout
problem, I have a bunch and you can have some.
You can also buy them new 3d-printed.
http://shpws.me/QgAT
--
bkw
