I had seen Big Ol Mess O' wires write up about the Tranz Mozart.  It was a modified TRANZ 330 that would read the magnetic stripe on a credit card and then play a tune based on the data it read.  I burned a ROM and tested it myself and it worked.  I then put the TRANZ on a shelf and for about about a decade it sat. 

When I saw the retro challenge I thought that maybe I could do something more with the TRANZ POS machine.  Maybe a game?  I was going to do a guess my pin game but it didn't use much of the TRANZ's capabilities.

The Tranz300 has:

Z80 Processor running at about 4 mhz.

32K of RAM

32K of ROM

16 Button Key pad

16 Character Vacuum Fluorescent Display

2 Serial ports operating up to 9600 baud

Telco and Telephone ports

Magnetic Strip Reader

Real Time Clock

A very basic computer that you can pickup for $20.00.

I have a modest telescope and like to look at the planets.  There are plenty of ways and web sites to help in determining when and where the planets will be at any time. This gave me the idea for this project.  I could do this and use almost all the features of the TRANZ 330.  (I could have useed the magnetic strip reader, but the amount of data it would hold really didn't provide much other than maybe a pointer for a look up table.  Swipe a card that has star's name on it and have the Z80 look up data in  a look up table.  Not really an exercise.  I could use the Real Time Clock,  but if a travel, I'd have to update it whenever I move to another timezone.  I would have to use a GPS anyways and I could use the time info from it so a RTC wasn't needed.

With an idea in my mind I set about building the project.  I purchase a GPS module,  grabbed all the UV-EPROMs I had,  my programmer and got to work.  I needed to get the display working first as it would be used later to troubleshoot later on.  One thing I noticed at this time is that knowing how write assembler and actually writing assembler  for the Z80 are to different things.  I've done assembly on PIC chips,  but I had easy access to books and documentation.  I have no books on the Z80.  This where I relied on chatGPT for help.  I could ask it to intialize the display driver chip and display an "H" on the display.  I could then do the rest of the "HELLO" test.  

Tracing, lots of tracing.  I had to make sure that I knew where the serial ports went to what part of the DART (Dual Asynchronous Receiver Transmitter)  chip.  Then I could ask chatGPT to initialize a serial port and prcoeed with sending a receiving data.  Baby steps, lots of baby steps.  Thankfully I had those UV-EPROMs.

With the serial port figured out I could now add a GPS.  But wait, these ports are RS232 not TTL.  Found that out with a multimeter and not with a burnt GPS module.  A MAX3232 line driver/reciever IC fixed that.  Bought a breakout board from Sparkfun and problem solved.   Also, the GPS and the breakout board need 5 volts and there is no 5 volts brought out on the serial port.  During the tracing,  I found out that not only wasn't pin 8 of the DIN8 connector unused it didn't have a trace leading to or from the pad.  A simple piece of wire soldered to a nearby pin and the GPS was happily sending data.  Baby steps.

Things went a lot faster after that.  Bigger baby steps.  I could easily receive and display my GPS info and the printer wasn't presenting any difficulties.  Soon I could display a splash screen,  get location data and print and or display results.  I had a routine from my pic projects that would perform ephemeris calculations using GPS data so I just gave it to chatGPT and it gave me back a fully working-

No, it didn't.  The data didn't match what I could get from the Heavens Above website.  I had to baby step again.  It doesn't help when...