REX# does not provide any software main rom feature, only REX Classic does.
You can use a FlexROM as just an ordinary re-writable rom to replace the
stock one, but you would need to open up the machine to re-write the
eeprom (or flash, there is also a flash version). You just install a
jumper on the /CS pins which has the effect of just connecting the /cs
pin from the bus directly to the /cs pin on the eeprom like normal.
To get a software main rom, you need a REX Classic.
You write a normal main rom to the chip and install it like normal, but
you connect two wires to the /CS pins instead of a jumper. Run the two
wires out to the option rom compartment, just fish them both through one
of the little holes where the compartment door tabs go. Keep track of
which wire is the /CS_OUT one. Label it REX TP1 on the end in the
compartment. That is the one that connects to the bus, and that is the
one that needs to be connected to the TP1 pin on the REX, but don't
connect it initially. Leave the other wire disconnected. Don't put it on
the TP2 pin.
Close up the machine. You don't need to go inside again.
Initially, connect the two wires to each other in the option rom
compartment. IE with a short male-male dupont wire, or just any plain
solid wire that has a thick enough guage to stick in the female dupont
wire ends. This causes the machine to boot from the main rom on the
flexrom inside the machine.
Boot the machine and activate the REX by the usual CALL 63012
Find the y2k T102 main rom image from the flexrom wiki page, and like
described there, make 2 copies of the Y2K fixed T102 main rom image, and
hex edit them to change the text displayed in the copyright banner in
BASIC, just so that later you have a way to see which rom you are
actually running.
In REXMGR, hit tab until you get to the SYS screen, and load the
priimary and secondary main rom images via TPDD the same as loading
option rom images or ram backup images.
Now shut the machine off and connect the /CS_OUT wire to the REX TP1.
Leave the other wire disconnected. Don't put it on the TP2 pin.
Now boot the machine and go into BASIC and see the altered banner.
Going forward, you can keep reloading hacked versions of main rom images
into either the primary or secondary slots, or both, since the flexrom
wire ends up acting as a 3rd ultimate fallback so you can always boot
even if you totally screw up both primary and secondary slots. You Can't
break the internal main rom no matter what you do with the rex. The only
way to edit the internal main rom is to open the machine back up and
connect it to a programmer.
It's actually super convenient once it's set up. REX makes it a breeze
to load the images, and having 2 slots means you can keep one slot
sacrosanct and only hack on the other slot, so you can recover from
borked hacks without even having to open the option rom compartment and
switch the wires.
Without a REX Classic, you can still re-write the rom, but only by
connecting it to a programmer, so it needs the machine to be opened up.
The pics show using a SOIC test clip, but there is also a programming
adapter pcb you can make instead.
https://github.com/bkw777/aDIPters#flexrom_100
https://github.com/bkw777/aDIPters#flexrom_100-programming-adapter
Or for the flash version, because the 28C256 eeprom is getting
ridiculous expensive these days.:
https://github.com/bkw777/aDIPters#flashrom_100
https://github.com/bkw777/aDIPters#flashrom_100-programming-adapter
--
bkw
On 11/12/23 17:07, runrin wrote:
Hi all,
I've got a REX# in my m100 and was wondering if it was compatible with
the FlexROM, which I see uses some jumper cables to interface with the
original REX. The REX# doesn't seem to have the pins to connect those
jumpers.
My priority is changing the keymap for the m100 since I don't use
QWERTY, but being able to hack the ROM right from the machine with the
REX seems like a nice feature. I will likely order a FlexROM board
anyway, since it seems like the best option to swap my LH535618 system
rom.
Has anyone had any success getting the FlexROM working with the REX#?
Any tips would be appreciated. I don't mind hacking the REX# with bodge
wires if that's what I have to do.
If anyone has other suggestions for the best way to swap the rom, it's
unlikely I will be doing it regularly once I have my keymap working the
way I want, so I'd be open for suggestions there too.
Thanks!
--
bkw
