Re: [comp.sys.cbm] New commodore hard drive controller

From: Hársfalvi Levente (
Date: 2002-08-22 11:02:19


Asbjørn Djupdal wrote:

> But I can't see how to get rid of the 7406 chip.

That's pretty simple. You can use the AVR portbits like they were open
collector outputs: set the respective output bits (PORTD.0 and PORTD.1)
to '0's, and activate them using the data direction register when it's
neccessary (DDRD.0 and DDRD.1). With DDRD.0 =1, the pin is output (= a
strong 0 level), with DDRD.0 = 0 the pin is input ( = the pin is left
floating) and you can read its value from PIND.0 . That's probably all
about it.

There's a small chance that it won't be able to drive as many units on
the IEC bus as the 7406 could (as the 7406 can sink more current). But
from the safety's side, there shouldn't be any problems. The AVR
portpins are well protected, the whole unit is pretty robust. Sometimes
I've put AVRs with reverse alignment into the IC socket, and they all
survived the accident without problems :-). If that, they should survive
most accidents ;-).

> Btw, this is my first hardware design.

Cool :-).

BTW, if it were smaller, it could call for a CompactFlash as media,
rather than an old IDE HDD. If something at all, I especially like the
noiseless operation of these old computers.



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