I was probably a bit silly to buy my first Lexitron word processor, but to buy a second was bordering on madness.
I was thinking that i would grab some spares for my existing machine, perhaps including a keyboard with working microcontroller.
As with my first purchase, this was a secondary item – i went to collect an IBM 5160. These machines seem to find me because when i got there, i found that there were two of them.
They were located very high up on top of two bookshelves in a shed that was so full of stuff that they could barely be accessed at all. My back survived.
Naturally, they turned into a project, resulting in one good unit, a set of spares, and some answers to unanswered questions.
It was never my intention to buy this machine. I drove out to Lewiston (just north of Adelaide) to collect another purchase, and the seller asked if i would be interested in this mammoth. It had apparently come from a South Australian government department, but had been subsequently used by the seller and his family for several years during the eighties.
I did some quick research and found that it was a word processor – not really my cup of tea. In the end, i bought it for about the value of the two drives. It also came with a daisy wheel printer, a long and heavy-duty printer cable, a couple of manuals and some beaten up looking disks. The screen looked like it had some kind of disease, which was later identified as CRT cataracts.
I was happy to find that the drives were Shugart SA400 drives because these are the first really successful 5.25″ drives.
Backing up the disks was an exercise in itself, but once done, i set the machine to work. I replaced a shorted tantalum and gave the drives some love. I started the machine up and, surprisingly, the machine booted into its word processing program.
Mild joy was short-lived: the keyboard did not work, and it was the microcontroller that had failed. At this point i should have pulled the drives and some other spares and sent it off to the recyclers. Instead, i built a teensy based replacement for the microcontroller and reverse engineered the keyboard. This act of madness yielded a system that was close enough to demonstrate the machine as a word processor.
Along the way, i had picked up hints of CP/M being available for this machine. I periodically did google searches to see if there might be some images kicking around and to my surprise about 3 years later they appeared on archive.org (thanks to the person who did that – dasher perhaps).
Once written, with some help from an Adelaide Retro Computing Group member (thanks Mick S), the machine was able to boot to CP/M and take on a new life as a computer.
If the success of a vintage computing purchase is measured by the hours endured to get it working (the primary entertainment value), then this machine has certainly delivered.
For a little history of Lexitron see the video here:
The System 80 is an attempt, largely successful, to create a machine compatible with the TRS-80 Model I.
Terry Stewart has done a wonderful job of documenting the System 80. Everything that you could ever want to know about it is there. I’ll just focus on my own experience.
I bought this machine from a colleague, Scott, at the Adelaide Retro Computing Group back in 2020. My recollection is that he had collected a number of computers from a seller. This one was outside his interests, so he offered it for sale. I was happy to take it; i never expected to have such an opportunity.
The machine came with an expansion unit and a floppy disk drive. The expansion unit, X4010, has a three slot S-100 backplane. It provides 32k of memory, a disk controller, RS232 port and printer port.
The machine can run any of the myriad of operating systems that were created for the TRS-80 Model 1. Similarly, it can load programs from cassette, just as the TRS-80 Model I can.
This particular machine is an early version with no tape level meter. It has a keyboard modification that replaces one of the shift keys with backspace and tab keys.
It came with a soft plastic dust cover. Instead of protecting the unit, it caused a lot of unsightly “melts” in the plastic. There were also several other issues to work through.
The computer is badged as a “third generation computer” but, as far as i can work out, it would normally be considered a fourth generation computer. Perhaps the usage of the term changed. Or perhaps it is the only example of “underselling” in the computer industry.
The 7500 system uses a 5.25” drive rather than an 8″. As it turns out, the floppy disk drive in this unit, Mitsubishi 4854-342, is intended as an 8″ replacement – it even claims to be a 77 track drive although i suspect it’s good for 80.
The 50 pin host interface is connected to the 34 pin drive interface via a simple adapter. All up, this means that the 8” images can be written to HD 5.25” disks.
Looking at the simple 50/34 adapter board, I suspect that the drive has a couple of signals that may not be present on a 5.25” interface – Ready and 2Sides. I imagine that 2Sides is always asserted because there is no way for a 5.25″ drive to know if a disk is single sided. 8″ drives can.
The drive was cleaned and lubricated and tested ok with Imagedisk.
8” Pin
8” SIgnal
5.25” Pin
5.25” Adapter
Comments for Emulation with Gotek
2
TG43_L
Not used
4
6
8
10
2SIDES_L
2
REDWC_L
Not driven by controller or gotek. Pull down
12
14
SIDESEL
32
SIDESEL
16
18
HEADLOAD_L
4
Not Used
20
INDEX_L
8
INDEX_L
22
READY_L
34
DISKCHG_L
24
26
DS0
10
DS0
28
DS1
12
DS1
30
DS2
14
DS2
32
DS3
6
DS3
34
DIRC_L
18
DIRC_L
36
STEP_L
20
STEP_L
38
WDATA_L
22
WDATA_L
40
WGATE_L
24
WGATE_L
42
TRACK0_L
26
TRACK0_L
44
WRTPRT_L
28
WRTPRT_L
46
RDATA_L
30
RDATA_L
48
50
16
MOTORON
I wrote an HD floppy disk from 8″ disk image 8_257_02 (Pulsar Turbo V1.3 Master Configuration Sys 14 Config V24 Single User) using greaseweazle.
