Now that the replica of the first computer I ever owned and built is finished (see my 2650 replica), it is time to move on to the first computer I ever used – the TRS-80 Model 1. I spent most of the school Christmas holidays of 1977 in my local Tandy store becoming an expert on this device. Computers have been my career and hobby ever since.

I never actually owned a Model 1 until a few years ago when I acquired two fully operating systems, one with an expansion interface and drives. I’d like a Model 3 and a Model 4, but they are getting hard to find on eBay, and expensive, Besides, I don’t have the room for them all!

There are software emulators for these machines, but that doesn’t fulfill the inner hardware nerd. I want to build something.

There are other TRS-80 replica projects. This guy is building a replica of the Model 1 as close as possible to the original using discrete logic. I like that idea – I recently built the excellent PC-Retro from MTM Scientific. I also found this project with but it has not been updated since 2015.

I’ve decided to build a TRS-80 replica using an FPGA to implement the Z80 core, video generator and most of the I/O and emulation logic, with an Arduino to handle the SD-Card and associated FAT file system. Here is what it will look like:

The intention is to emulate the Model 1, 3 and 4. On-screen menus will be used to select various options. VGA and composite output will be included, and probably HDMI as well. A standard PC keyboard can be used, or a memory-mapped TRS-80 keyboard can be attached. Floppy disks will be emulated by the Arduino, and I’l include a socket for 17xx/27xx controller chip as well.

I’ve got the basic video timing working with a Xilinx Spartan 3 FPGA (see below) and the next step is include the Z80 core and a ROM image. Eagle eyed readers will see slight artifacts on the bottom of the second row of graphics characters – they will be fixed!

I’m open to suggestions and comments. Please email to craig@postincrement.com or the various Facebook groups dedicated to the TRS-80 and DIY Z-80