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Loading Model III ROMS on a 4P

tempest

tempest

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I think (fingers crossed) that I'm going to be coming into possession of a Model 4P soon. One thing that always confused me about the 4P is that you have to load the Model III rom from a boot disk. Can someone explain to me exactly how this is done? For example, on a Model III there are two common scenarios:

1. If I wanted to play an auto-booting game I'd just stick it in and turn the system on and the game auto-loads.
2. If the game requires a DOS, I'd boot up to that and then insert the disk with my game on it and execute it.

So since the Model 4P doesn't have the Model III rom, how does this work? Do I have to insert the disk with the Model III rom file first THEN continue as normal? Do I still need to do this if I'm just booting a DOS (scenario 2) or is this just for auto-booting games (scenario 1)? Neither is a big deal, I'm just curious.
 
The 4P can operate in Model III or Model 4 mode. Model 4 mode is for DOSes that don't need the Model III ROM such as LS-DOS. Model III mode is for anything that's Model III compatible such as LDOS or Model III games. It's possible that some self-booting Model III game floppies might not need the ROM.

The 4P contains a small boot ROM but no Model III ROM with BASIC and miscellaneous other functions. The boot ROM allows booting from floppy, hard drive, or even RS-232 (it also contains a nonfunctional ArcNET boot option.)

To boot into Model III mode you need a TRS-DOS 1.3 formatted floppy containing (at least) the file MODELA/III, which is the MODEL III ROM in load-file format. You put this in drive :0 (door open if powered down), power on or reset the 4P, close the drive :0 door, then press <3> and <P> within the 3-second boot pause. The 4P will load the ROM into its RAM, set that RAM block to read-only, and prompt for your boot floppy.

The <3> causes the 4P's boot ROM to load the Model III ROM file. The <P> tells it to prompt for the boot floppy once that's complete. Without the <P> it'll say something about a non-system disk; you can then insert your boot floppy and hit reset instead.

Once the ROM is loaded you can reset the machine to boot from floppy without repeating the first step.

Or you could get a M3SE, which can load the Model III ROM file from its hard drive:
http://BartlettLabs.com/M3SE
 
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Ok a few (ok, a lot) questions:

1. You don't close the drive door until after you power on the 4P? Any reason for that?

2. Could you have the MODELA/III rom on a disk with TRS-DOS so you don't have to swap disks or will that not fit?

3. What do the <3> and <P> keys do (do you press them together or separate)? I think I read that the <3> key loads the system into Model III mode, but what about the <P> key?

4. Once the ROM is loaded into the read only RAM, does it stay in memory until power down?

5. Do most games require model III mode or will they work in model 4 mode?


Wow that M3SE project sounds neat! I'll have to watch that page.

EDIT: I think I may have seen the Model I version of this at VCFMW and not known it. I remember talking to him about his TRS-80 stuff (I tried to get his Model III for my C128D). http://bartlettlabs.com/MISE/index.html
 
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1. Powering on any TRS-80 with a floppy in a closed drive can damage the floppy or its contents.

2. If you have a TRS-DOS 1.3 boot floppy, it should already have the MODELA/III file on it, so you can just boot that directly without swapping disks.

3. You press the keys one at a time. I updated my initial reply with more info about this. The <3> key tells the 4P to load the Model III ROM from floppy. The <P> tells it to prompt for a boot floppy when the ROM has been loaded. There are a number of other keys that can be pressed during the boot pause, such as <1> to boot from hard disk, <2> to force a floppy boot, <V> to show the boot ROM version, and others.

4. You shouldn't need to reload the Model III ROM while the machine stays powered up. If it gets corrupted somehow you can hit <L> after reset to force a reload.

5. I would guess most games for the Model III need the ROM, but there could be some that don't.

Yeah that's me... the pen name seemed like a good idea when I set up my account here and I can't seem to change it now... and I still want a C128D.
 
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Oh that's you! Small world! :)

I still have that 128D if you're interested in some sort of TRS-80 related trade (a Model III or 4). :) It's just going to waste here since I have my regular C64 hooked up.
 
Joe Zwerko said:
Yeah that's me... the pen name seemed like a good idea when I set up my account here and I can't seem to change it now... and I still want a C128D.
Click to expand...

The Mayor McCheese avatar should have given it away!
 
Actually that's a "selfie". Any resemblance to trademarked characters is completely coincidental.
 
So I got my 4P today and I found that the Model III LDOS disk I was using for my games (5.3.1) didn't have the ModelIII/A rom on it. So using a disk utility (Super Utility 4/4P) I was able to delete a file (readme.txt) to free up enough room to copy the Model III rom file over. This all worked out great. Oddly enough however the 4P now automatically boots the ROM when I have that disk in there, I don't have to push 3. Is this because it's a Model III disk and it auto detects that somehow? Whatever is causing it, it's all kinds of handy to just put the disk in the drive and have it auto boot into LDOS.
 
Tried that myself just now, and it worked as you said... odd how I was always under the impression that it had to be a TRS-DOS 1.3 diskette.

Anyway, with M3SE on a 4P, no diskette at all is needed, and it boots a lot faster. And you get hard drives. And Ethernet. And stuff.

Finding hats that fit is difficult...
 
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The FreHD also loads the model3 rom file if it is found on the FAT filesystem. Just FYI.

-Fred
 
The Model 4P is a nifty little machine with quite a few tricks on its sleeve.

When reading the MODELA/III file, the CPU reads instructions from the boot-rom, while it writes the file in RAM in exactly the same address-range at the same time. After finishing the complete file the ROM is switched out and RAM becomes read/write. Not unique but I've seen it seldom before.

Nicest trick is that more and different ROM-files can be present on the disk, and can be selected by a key-press during boot. If you press B the file MODELB/III will be loaded, if you press C MODELC/III etc up to the letter G. So it tests against MODEL%/III. Perfect for those tinkering with OS's and drivers!

Last trick is that it is capable of reading from disk in different formats (both TRS-DOS 1.x and LDOS-style), so disks with tracks starting with sector 1 and those starting with sector 0.
 
BartH said:
Last trick is that it is capable of reading from disk in different formats (both TRS-DOS 1.x and LDOS-style), so disks with tracks starting with sector 1 and those starting with sector 0.
Click to expand...

Aren't all TRS-80's capable of reading both styles?
 
My guess is that he means that the 4p can read a LDOS disk with trsdos 1.x loaded? Or reading a trsdos 1.x with LDOS loaded? Not to sure I know the desktop 4 can't
do that.
 
BartH said:
...
Last trick is that [the boot ROM] is capable of reading [the MODELx/III ROM image file] from disk in different formats (both TRS-DOS 1.x and LDOS-style), so disks with tracks starting with sector 1 and those starting with sector 0.
Click to expand...

Let me add in some useful info in brackets to clarify what I think you meant...... the boot ROM can read the ROM image file from both LDOS-style and Model III TRSDOS-style disks. This is not exactly trivial, since the directory records, GAT, HIT, pointers within the directory records, BOOT/SYS first sector data fields required to find the directory track, etc, are different between them. Frank (Durda IV) did a bang-up job writing the ROM load code in the space that it takes.
 
lowen said:
Let me add in some useful info in brackets to clarify what I think you meant...... the boot ROM can read the ROM image file from both LDOS-style and Model III TRSDOS-style disks. This is not exactly trivial, since the directory records, GAT, HIT, pointers within the directory records, BOOT/SYS first sector data fields required to find the directory track, etc, are different between them. Frank (Durda IV) did a bang-up job writing the ROM load code in the space that it takes.
Click to expand...
I'm sorry I wasn't clear on this, lowen is right. The boot-rom is capable of reading both formats and that is a very neat trick!
This and the possibility of using different MODEL%/III files makes it a perfect machine for tinkering with OS's.
 
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