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Upgrading a TRS80 Model 4P

J

jltursan

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Sep 24, 2010
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Madrid, Spain
As promised, I've uploaded some photos of my recently fixed/upgraded Model 4P.

My 4P second drive has been broken since long time ago; so it was a great chance to not only fix it; but to completely replace the drive with a 3.5" one. First one the cable:



As simple as replacing one of the 5.25" connectors with a new 3.5" IDC type. Of course, one of the internal 5.25" type molex power plugs needed a replacement; but, instead, I used a 5.25" to 3.5" molex converter to do the trick.

Next, the 4P drive case and the 3.5" to 5.25" bay converter:



Yes, the 4P drive holder needed some work. I was forced to drill a new set of holes to screw in place the 3.5" converter and 360K 5.25" drive. Also, the converter and 3.5" drive were white; so they needed some black painting...

Here're the new drives assembled back in the main body:



To test the new drive, nothing better than boot with a TRSDOS dumped to a 3.5" floppy:



Meanwhile, surfing the web, I noticed how easy is to upgrade my 4P model to 128K; so with some 1x64K ICs (to be exact, 8 x MN4164P-15A) and a jumper the task was quickly finished. Below, CP/M 2.31 has finished loading from a 3.5" floppy and the 64K M: ramdrive appears empty in all its glory:



Sadly I don't know of any other software that takes profit from this upgraded memory; so that's all...

Now, I want to look for info about the date internals of the 4P+TRSDOS. The date, once inserted is lost inmediately when shutting down the machine; so I suposse that if there's a clock IC, it's battery must be empty. Also, TRSDOS doesn't accept any date over 1987; so as I've read about a patch, I'll try to fix it.

And the yellowing.....; yes, the computer is heavily yellowed; but maybe a bit of retr0bright will make some good for it some day...

Btw, I apologize for my broken english, take it kindly...:ashamed:
 
They never had a battery for the date, it had to be entered everytime on boot. LSDOS will get you a bit further - my Dad used these well into the 1990's in business and used 1991 or 1992 (leap year depending!) as the date accordingly.

NB great work :D
 
LSDOS or L-DOS, with a patch will get you to 2079 or some such. ver 6.3.1J.
Check out Ira's site at www.trs-80.com, or when I get my hardware finished getting setup on my 4 and 4D I can make you a copy of mine.
Where did you get the chips for your memory upgrade?

¡buena materia!
 
No Dallas chip?...bummer..., well, I'll keep typing the date every startup... :|

I've never used LSDOS; but maybe is worth trying it...
Thanks for your kind offer dracos; but meanwhile I'll try to get a patch for TRSDOS, I'm sure that I've read something about :)

The RAM used is nothing fancy, standard 1x64K SRAM ICs, 4164 family. I've a lot of Panasonic SRAM ICs with access time of 150ns and they've proved to work fine until now.
I guess that other brands like TI or Hitachi would fit as well the upgrade.

Now, the only way to test the ramdrive that comes to my mind is filling the empty space copying files and checking for errors. I'm not aware of memory checker tools.
 
jltursan said:
Now, the only way to test the ramdrive that comes to my mind is filling the empty space copying files and checking for errors. I'm not aware of memory checker tools.
Click to expand...

I'm unfamiliar with ramdrives on a trs-80, used them quite a bit in MS-DOS though. What I would do is find a program disk that you usually use, is smaller than 64k, and requires a noticable amount of diskette write/reads, and copy that to the ramdrive, and run from there. Depending on how flexible they are, you might also be able just to move a programs data file there, if you want to keep it though, remember to copy back before you power off or reboot!

Hopefully I will be doing this on my 4 and 4D when I can find some chips.
 
LSDOS 6.3.x has built in support for years up to 2079. Also LSDOS 5.3.x I have used that version on my model I almost exclussively. A minor correction though the RAM is 64k x 1 DRAM not SRAM. Draocs Just get some 4164's can get at Jameco or other electronics parts distributers.
 
Nice machine.

I have a Model 4 (64k) and the chips I need to upgrade to 128. Haven't got around to it yet. As has been mentioned, there doesn't seem like a lot of software around that uses the expanded memory.

One thing that would be useful would be run the RAMDISK as the system disk for operations. I'm not sure this could be done though. The process would have to be..

1. Boot from LDOS or TRSDOS
2. Have a batch file which on boot set up the RAM disk and copied the System disk to it.
3. Configure the RAMDISK as drive 0.

I'm not sure if this possible with TRSDOS 6 or LDOS?

Tez
 
I guess it would be useful for e.g. SuperScripsit as I recall that using the drives quite a bit.
 
tezza said:
One thing that would be useful would be run the RAMDISK as the system disk for operations. I'm not sure this could be done though. The process would have to be..

1. Boot from LDOS or TRSDOS
2. Have a batch file which on boot set up the RAM disk and copied the System disk to it.
3. Configure the RAMDISK as drive 0.

I'm not sure if this possible with TRSDOS 6 or LDOS?

Tez
Click to expand...

I don't know either if that's possible with LSDOS, but I did exactly that with Montezuma Micro CP/M, back in the day. I wrote an ASM routine that resized the RAMDISK, copied the system tracks to the RAMDISK, then renumbered the drives so the RAMDISK was drive A: Warm restarts were practically instantaneous, and you no longer had to keep a system diskette in one of the drives.
 
Indeed, the ICs are DRAM, not SRAM...my bad.

Hey mloewen, it sounds pretty cool, do you still have that tool or at least the code?. It would be great at least to get a full CP/M system running from RAM.

All of this reminds me the 6809 OS9, it can load full commands (the so called "modules") to RAM to progressively transfer the SO out of the disk.
 
tezza said:
Yes, I would be interested in this too.

Tez
Click to expand...

The utility was called RAMBOOT, from November 1, 1985. It works with Montezuma Micro BIOS 2.21 and a couple of other versions before and after. It does NOT work with BIOS 2.31. If anyone is interested in a copy, send me a PM with your preferred email address.
 
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