80 columns on MZ700

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Joined: Wed Feb 07, 2018 4:41 pm

Re: 80 columns on MZ700

Post by sharpmz » Mon Feb 19, 2018 11:31 pm

25 years are gone, but, indeed, very very interesting. (btw, already implemented in Michael's emu).
I wonder that it was sold by a magazine in '95 and a hint in a mag of '90 that it is in work. No info between this mags, no further articles about it all the years.
I know such timing problems by old integrated circuits replaced by "modern" ones. John always does a very good job like Maurice did.
I also have several projects on hold. No time, we all have only one life, unfortunately ;)
Would be great if you can revive this project so that everyone can recreate it.

Posts: 30
Joined: Sun Feb 17, 2019 6:41 pm

Re: 80 columns on MZ700

Post by S_U_C » Tue Feb 26, 2019 3:41 pm

I design the SUC MZ700 80 column kit, and due to the interest shown on the forum I have look at it again, and found some possible solutions to the small dot problem caused by modern 74LS chips proagation delay is no longer 9nS.
In fact the 700 did not require a frequence doubler as the CLOCK frequency is already the 2x the nornal seriliser frequency.
There are some other solutions, and I have writen about them in the Sharp User Club 2019 vol 1 magazine that will be out in the next few months.

Posts: 30
Joined: Sun Feb 17, 2019 6:41 pm

Re: 80 columns on MZ700

Post by S_U_C » Sun Jul 07, 2019 12:55 pm

I have look at my 80-column design and there are 2 options to cure the small dot problem caused by the faster modern chips.
1) increase the number of gates in the delay chain (the XOR gates have 2 times the delay as the invertors) we need 27nS
so 3 spare XOR gates wired as buffers is 6 delays about 20nS and 2 invertors is about right. there is enough spare gates to do this.

2) remove the frequency doubler and use the mainboards 17.73 MHz as the 2x frequency, you will have to buffer the loading on the 17.73 MHz oscillator.

Full article in the 2019 vol1 issue if the SUC magazine.

John Edwards Sharp Users Club

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