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These kinds of channels are gold.

Chap that's a weird approach to debounce a key, using Schmidt trigger : debounce is done in software, using a very simple state machine..... No exotic part like xx14, which is expensive, are allowed. Think of an automotive application, like a climate control panel with scores of keys: your approach would dictate use of a Schmidt trigger for each key an increase in cost of bill of material not tolerated........ 😮😮😮

Great video. I just ordered a static ram to play with, arrived today. Then this video popped up and you are using the exactsame chip ... lol. I am just getting back into the hobby, never did use a static ram, they were super expensive 40 years ago. I did do a breadboard memory upgrade for my Trs80 Model 1 using 64k x 1 dynamic ram chips. I only used half the memory. A lot of wires and it surprisingly worked. Got my z80 on order for some future use, not sure what yet.

A daughter come to her father and says: "Daddy, I want a pony!" Then the man says: "Sure Honey, I will get one for you." I can almost feel the joy when she gets the computer fully assembled and tested.

What a cliffhanger... Will there be any update? I am pretty curious what went wrong with the memory card design...

i would have all the ic's pointing the same way

I tried 5v power supply to my ne555 chip, and set R1=R2=150 ohm. Without capacitor being inserted into the board, the output frequency approached 1MHz. But the frequency was unstable. Without C ?? I assume there must be a few pF parasite capacitance on the board wire connection... After I put a 68nF capacitor in place, the output frequency dropped to 170kHz... Stable frequency.

Really, is there a static version of Z80? All that I could find stopped working at 1-200 Hz.

Can it play River Raid ?

The best explanation of the Z80 basics so far! Very well explained 👌

Thank you for doing this. I got my LCD working using the first code you went over. How ever please post your final code on the LCD because the link is broken and it was more optimized. Watching you do the assembly helped me learn a lot. Thanks so much again.

YES! LIVE STREAM IT. MIKE

I notice you ran the reset (low) from the CPU threw the not gate and then to the transistor which creates the hl PWR signal. Should this PWR signal go to VDD and also the "A" pin on the LCD to cut power to the back light as well? Just sending PWR to the Vdd pin will only turn power off to the LCD and reset it but leaves the power on the back light.

I am going to try your LCD display and add it to my z80 with 28c16 rom and 62256 Ram. However is there a way to get a copy of your last code on the LCD display. The link on the website that suppose to have the code seems broken. I followed the entire video up to the very last or just past the part the had the bust bit code. I thought you would really make a great teacher. Its really fun doing the Z80 build and I have learned alot from your sharing.

Hi this is Harvey from PCBWay and we wonder if you are interested in doin some project with us?

Cool 😎👍

glad I found this channel.

I would love to see a live stream!

👋🏽 I'd happily watch an electronics livestream 😮, good luck in the build

I think there is a fundamental problem with backplanes using SIL connectors. They are fine for DC signals but running them at 4Mhz plus, I feel is starting to create issues? There’s a reason RF connectors are very precisely designed. That and the lack of grounds used in every hobbyist design, you look at FPGA boards and every other pin is a ground connection. I think the problem is falling between two schools, where because the signals are relatively slow, so we assume they are just going to work without issues

Try moving the boards around … one on each end of the backplane

I had these issue and pull up or down resistors were needed to stop the traces from cross talking and behaving like an antenna gather all sorts of noise

i understand you can page 255 time from one IO and there 255 IO so if you have 8k rom and magic rest use 56k ram and paging ram you can have 3641.4 MB/3.6GB ram 255*255*56k on z80 if you want build damn thing lol and program some software to use it. mayby notepad LOL and we did not need page rom at all xD rom you have your notepad that use pages of ram to write huge book xD

Thank you ... Your video is very useful as I am designing the dream computer I couldn't afford when I was 12 in 1982. And I'm building from scratch, all the resources I can find are welcome, and your work just took a major spot in my project. Thanks Bonjour from France.

I like the Pony80, I see it as a small reliable workhorse.

couldnt figure out why my computer didnt work, finally realised that just because my clock signal was blinking it dosent mean that the chip was getting a zero when the light went off so i tied it trough a resistor and now ram rom and cpu works just fine.

Hey!! The HCT245 is a real workhorse for the data bus. And it’s tri-state AND bi-directional. I use those every chance I get on my Z80 projects. And the HCT244 makes a great address bus driver too! Fast and they take most of the load off the Z80. Well done! Looking forward to the video.

Leave the capacitor out and the frequency will be higher. New (fake Chinese) NE555's are quite a bit faster than old genuine American made parts because of the modern fine line construction. Ron W4BIN

Hello! use ld sp,0 instead of $ffff otherwise you will miss address $ffff, because push first decrements the sp then store the actual half of the pair AF into the (SP). Greets from Romania!

I’d imagine those really long ribbon cables will be part of the problem? Although I remember using ridiculously long SCSI cables back in the day, but they were twisted ribbon with lots of grounds and clad in copper foil

Great video , I am a big fan of the Z80, 8088 & 6502 CPUs and worked on them in the 80s' . The NMI interrupt can also be useful for the 'BREAK/Pause' key on a keyboard to soft reset when needed to break out of a running program. Many thanks and is very nice to see these videos.

I’d like to see your code for those displays. I’m hanging one on my project. Did you memory map them or are they on the I/O as an output only? Thanks!

There are different RETurn instructions for the NMI v INT v call … to reset the states properly…

So, I see you found the issue with the LCD. I think I missed the video explaining your debug process.

The primary reason for the alternative registers was for interrupt processing… on the 8080, pushes to the stack for all of the regs had to be done causing dozens of instructions instead of one

Great material, thanks for spending the time and resource explaining deep down the logic and hardware for the Z80, appreciated !

On this arch, we had a card that had a button on it that triggered an NMI and code that provided a debugger to the pc…

I primarily work on IBM mainframes and although they aren’t called interrupts, it has similar services… IO, SVC, Program Check, machine check all have a vectored address to service the request.

The S100 forums have a lot of solid info on bus termination, because they had to deal with such a long bus and cope with differing speed devices and loading. I quite like the active termination ideas

Thanks Bob, I'm enjoying this series very much. It's encouraging to see that I'm not the only one who gets these "surprises" along the way. Unlike me, you don't seem to swear much during the debugging process. :) In the video, you mention adding bus terminating resistors to the CPU board. Isn't that the "driver" side of the bus? I looked at your schematic and see the terminating resistors. Are these already in place on the board on the video? Where were you putting the breadboard resistor packs in this video? Keep it up! I'm learning more with every episode.

Regarding pads, best to check the data sheet for the devices in question - 1mm might be too tight for certain headers. Conversely, if you've got a narrow pinout TO92 transistor 1mm will be too large. I've been using Kicad and often draw my own footprints as I also like to have a decent bit of copper for soldering, particularly if the part will get some mechanical use - sockets and switches etc. Not sure if EasyEDA allows it but if you can build your own custom library of footprints you can set everything exactly how you like it.

I have not seen the schematics for your system. Since you are driving a bus, do you have HCT244’s (2x) to drive the address bus and a HCT245 to drive the data bus? There’s only so much current the Z80 can source or sink, and the Z80 needs some help to drive the lines. For the HCT245 use RD(NOT) to steer the direction. Also, there’s some reflection (standing waves) on unterminated lines. If you put the 10K single inline resistors on the address and data lines, they should be on the backplane board. Typical pull down is 4.7K and pull up is 10K. I’m designing a Z80 project right now using Mode 3 interrupts and all Z80 family of chips. Be sure to try out those bus transmitters (244) and bus transceiver (245) ICs. They have saved me a lot of heartburn. I’ve been designing stuff with the Z80 since 1981 or thereabouts. Good luck! Looking forward to your next video.

So simple and basic. A simple logic probe will save you a lot of trouble when it comes to tracking down poor or bad connections. The Z80 is good for control applications. Personally I'd forget about trying to maximize ram by bank switching. Thats a poor technique and adds unnecessary complexity. figure 1 or 2k for the stack and another 1k for IRQs. When you start writing assembly language or binary to memory by hand you'll find 64k is plenty of ram. I think when everything is said and done your entire program plus the ram required for temporary data storage is going to be way under 8k, probably in the 2 or 3k range plus an extra 1k for temporary storage. I'd consider a few 74ls373's to monitor the control and status signals of the cpu, and setting up a way to single step the cpu. I don't want to rain on your parade but I don't see a single decoupling capacitor on the board. I say those are necessary unless you want random problems occurring in the execution of your program. Remember the CPU has a fanout of 1, an important consideration when designing a computer with a lot of chips connected to the address and data bus. Personally I'd think about using a single 64kx8 static ram, and using a Raspberry pi or pi pico to put the cpu into the high impedance state and writing the code directly into ram by having the pi take control and perform a DMA operation. That's just me. It's your baby so you can do it anyway you want. I've done quite a few of these in the past, but my advice and or criticism will only get you a cup of coffee if I have 2 bucks to go with it. Don't let anyone get your feathers up. Never accept criticism from anyone you wouldn't take advice from. That's always worked for me. Don't get stuck thinking there's only one way to do something. I've been down that road. Maybe sometime in the future you'll consider using the MC68000 for a project after you've done a few Z80 projects. Peace out dude.

Floating issue …

Looks like a reflection problem. Your resistor network acts as termination. Pulling up or pulling down your address and data lines will of course help. Have you tried putting the CPU card on one end of the backplane, and another, like the memory card, on the other end?

One hint … on the dip sockets … I usually bend two pins top left, bottom right slightly to secure them … then flip the board

As soon as I saw that I was going something must be floating, then you said something must be floating. But if something was floating your mem check should fail (if written in a way that would detect correctly), maybe something to do with impedence on the bus that the termination resistors fix?? I don't know.

Reminds of "the ghost in the system" :)

Serial PWM modem and bbs

Random question, but what kind of surface are you working on here? Looks to be carbon fiber, is that a laminate or an actual carbon fiber table? It's quite nice. :p