Alioth's Journal: [Z80] Megahurts

This evening, I decided to add a crystal oscillator and clock divider (i.e. a 4520 counter) to some spare space on the board which I soldered up the 16 bit counter with tristate outputs. Basically, I soldered the circuit up such that you put a jumper on either the output of the crystal oscillator, or one of the 8 outputs from the 4520. This sends the square wave signal to two output pins - one via an inverter (NOT gate), and one straight - so there's both the clock signal and an inverted version of the same signal available.

The oscillator is made of a 4MHz crystal, one gate of a 4049 inverter, a resistor and a couple of 22pF capacitors. Putting the jumper on the output gives you 4MHz out at the output connector. Putting the jumper on subsequent pins of the 4520 counter gives 2MHz down to 15.625kHz.

So I disconnected the 555 timer I had been using to clock the Z80. First, I tried 1MHz. This worked fine. So I tried 2MHz. This also worked fine. So I tried 4MHz - which didn't work last night - and this worked. The CPU was certainly working fine, but now it was sending data to the LCD too fast for the LCD controller to handle, so every other character was getting dropped. This shows the reason why it didn't work with the 4MHz clock last night was probably because the crystal oscillator being built on breadboard wasn't giving a good enough square wave output to run the processor. But it works great once soldered up on tri pad board.

I will probably run things at 2MHz until I build the circuit needed to hang the LCD off the CPU's bus (since reading the status will become easier since I won't have to tell the PIO to change the port direction).

Easy solution to enable running at 4Mhz.

[TechnoLust]

J u s t _ p u t _ a _ s p a c e _ b e t w e e n _ e v e r y _ l e t t e r _ y o u _ s e n d !

Yes, I'm a software guy, not a hardware guy. :-) Also, /. apparently ignores  

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[Short Circuit]

Yeah, Slashdot ignores the nonbreaking space. Probably due to all the page-widening posts people were making back in the early days of Slashdot.

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[TechnoLust]

They should break after so many consecutive nbsps like they do if you type alkasjdhnfklajsdhflakjsdflajksdfljkasdflkajsdflkja sldfkjalsdkfjlaskjdflaksjfdlkasjfdlkajsfdlkajsfldk jalsdkjflaksjdflaksjfdlaksjfdlajsfdlkasjfdlaskjfdl aksfd see? that was just 1 series and it broke. Why do I have to think of everything? They need to start paying me to come up with this shit. :-)

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[Short Circuit]

--
"Da ist ein Technölüst in mein Unterpanten!"

What the hell were you doing in Eth's underpants?

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[TechnoLust]

He came home early.