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eZ-Tiny - Another New eZ80 Design [message #8672] Wed, 09 June 2021 10:29 Go to next message
wsm is currently offline  wsm
Messages: 232
Registered: February 2017
Location: AB, Canada
Senior Member
After designing and building my Min-eZ system that supports Ethernet etc., I realized it was also appropriate to design a more budget conscious eZ80 system. As a personal challenge I tried to make it fit into a very small case which worked well for the F92 and F93 variants but not the L92 variant. Although these three processors share the same footprint, the F92/F93 versions have flash memory and a maximum of 20 MHz whereas the L92 version is available at 50 MHz *BUT* has no internal flash for the reset (i.e. boot) code. All three processors have 4K or 8K of internal RAM that can be used for a banked common area.

The small two-sided board doesn't have enough space to add a boot device for the faster L92 variant so there's now a possibility for yet another unique system. However, I think I've reached my limit for miniaturization without going to four layers and/or BGA devices. If I redesign this with the required boot device I'll probably step up to the same size case as used for the MinZ-C system at approximately 2" x 2".

Case Size: 40mm x 40mm x 15mm or approximately 1.57" x 1.57" x 0.59"

Features:
- Zilog eZ80F92 or eZ80F93 at 18.432 MHz
- 128KB/64KB of internal flash memory for boot code, CP/M 2.2 and a 112KB/48KB "disk"
- 512KB or 2MB of zero-wait SRAM
- 8MB of serial flash as a resident flash "disk"
- Two USB serial ports with RTS/CTS handshaking and a default of 230400 baud
- MicroSD socket with SPI interface at 3MHz
- 256 bytes of EEPROM available for user programs
- Real Time Clock (RTC) with rechargeable battery
- A RUN (green) / HALT (red) bicolour LED
- A user-programmable LED
- A RESET pushbutton
- Optional ZDI debug header
- USB powered

The BIOS is a stripped down version of my Min-eZ BIOS but development is slow during our all too short summer months. My flash loader appears to be working so BIOS development and testing can continue. Thanks to pipelining, I'm predicting this system will be roughly the speed of a Z80 at 63-71 MHz or about 1.7 times the speed of a Z180 at 33 MHz.

As to availability ... the USB bridge is extremely scarce right now with long lead times or very high markups. I have a FEW of them and will be building a total of four of these systems but more than that will probably have to wait until around year end unless someone has some unused CP2105 chips that they'll sell to me at a reasonable price.

/forum/index.php?t=getfile&id=2185&private=0

The CF card at 42.8 x 36.4 mm is simply a size reference as this system uses a uSD card and not CF. There's also some parallax error due to the CF card being below the top of the system's case.
  • Attachment: eZ-Tiny.PNG
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Re: eZ-Tiny - Another New eZ80 Design [message #8863 is a reply to message #8672] Sat, 17 July 2021 09:24 Go to previous messageGo to next message
wsm is currently offline  wsm
Messages: 232
Registered: February 2017
Location: AB, Canada
Senior Member
The new BIOS appears to be working for all of the "disks" as is the ZDI debug interface. There are several subtle differences between the eZ80F92/93 and the eZ80F91 which I used on a previous design. One of these differences requires either a PCB revision or a jumper wire due to my oversight and bad assumption. The PCB files have been updated and will soon be sent for fabrication.

Performance appears to be about 3 times that of a Z180 at the same clock speed. ASCIIART takes about 27 seconds on a 36.864 MHz Z180 and about 18.4 seconds on the eZ-Tiny at 18.432 MHz.

Development is slow for me in the summer due to other activities. However I can foresee creating a cased version of the eZ80L92 or eZ80F91 at 50 MHz in the same case as the MinZ-C (2" square) but also including connectors for external I2C and SPI interfaces such as a graphic LCD. From a HW & SW perspective, the F91 is nicer to work with but it's also a TQ144 vs a VQ100 package. Time will tell ...

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Re: eZ-Tiny - Another New eZ80 Design [message #9381 is a reply to message #8863] Mon, 15 November 2021 14:23 Go to previous message
wsm is currently offline  wsm
Messages: 232
Registered: February 2017
Location: AB, Canada
Senior Member
Update: The aforementioned issue was corrected with PCB V1.1. I've been building this system and selling it on Tindie along with my other designs. There are four configurations: eZ80F92 or eZ80F93 and 512KB SRAM or 2MB SRAM. There is some online documentation <here>.

I have a V1.1 (i.e. latest revision) F92/512KB board that had a bad trace on it and I'll admit it was my soldering mistake. This has been repaired with a short piece of 30AWG Kynar wire and it has passed all of my testing.

/forum/index.php?t=getfile&id=2488&private=0

I'm offering this repaired system to members of this forum for $60 US which is about 1/2 my normal price. Shipping is included as is an SD card. PM me if interested

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