Without hardware accel blitting is never efficient.

I cannot download from that link you gave us. It's stuck at connecting to the site.

Perhaps you could try converting the files on the calculator at first launch? That way you don't distribute modified files, but rather a converter.

This is probably caused by a ground loop somewhere in your system.
http://en.wikipedia.org/wiki/Ground_loop_(electricity)

You cannot isolate grounds using resistors. The grounds are still electrically connected this way. Instead you could try using audio transformers or optocouplers to electrically isolate the signals. This technique is commonly used to get rid of ground loop interference.

Instead of isolating grounds you could also use differential inputs for the amplifiers. This requires an extra feedback loop on all input amplifiers.
http://en.wikipedia.org/wiki/Differential_amplifier#Operational_amplifier_as_differential_amplifier
With this method the voltage reference is no longer common ground, but the signal ground. You no longer need to connect all signal grounds together. Edit: They're not completely electrically isolated but you can set a very high input impedance, so they can barely affect eachother.

It always makes me jealous when I see one of these. I put some time and money into trying to make a z80 computer, but after a burned rom chip and 2 burned 9/5 v power converters, I gave up the project. 

I destroyed the UART chip today by applying power the wrong way around. Man that really pissed me off. It was such an awesome chip with two uart channels, FIFO buffer and tons of other cool features.
It forced me to go in a different direction with this computer though. I will use an eZ8 microcontroller for handling all I/O operations. The eZ8 has a lot of peripherals built in including two uart channels, timers, flash memory, adc, pwm. The only thing it lacks is the ability to execute machine code from ram. That's what the Z80 is for in this computer. The z80 will be the main CPU and the eZ8 only does the I/O.

Because the microcontroller needs time to respond to the z80 the z80 will be put in a halt state until the microcontroller is done processing the I/O request. This is similar to the way benryves solved this problem on his z80 computer.


This shows that breaking stuff is not always the end of the world.

You made a pretty looking tool I love stuff like this!

Z820 - Z80 Computer

Original post: http://8times8.eeems.me:81/blog/index-beta.php?thread=16

First video of a blinking LED program.


The features:
CPU: Z80 @ 20MHz
RAM: 128k
ROM: 8k (BIOS+BDOS)
UART: Up to 1.25Mb/s transfer rate
FDC: Not implemented yet.

Sourcecode can be found here: https://github.com/keoni29/z820 (unoptimized as all hell, cause I am still learning)

I hooked up a VGA video board to the computer. It's kinda slow since it uses the SPI bus, but it works.