Re: Noob question: examine arbitrary memory address? #ELF #memory


Hi Tor-Eirik,

I guess it's your design.  There's no better way of testing a project than by having a group build!  When you finish the corrections on the design, would you consider doing a board run for the group?

Josh Bensadon

From: <> on behalf of Tor-Eirik Lunde <teblunde@...>
Sent: Saturday, September 26, 2020 7:57 AM
To: <>
Subject: Re: [cosmacelf] Noob question: examine arbitrary memory address? #ELF #Memory
Yeah... I'm a bit of an amateur when it comes to electronics, so when it comes to faults I can just about figure out the logic of things. 

Nice going on finding a fix for the errors in my ways. Will have to revisit the design once I get a semblance of a hobby workshop up and running again 😀

lør. 26. sep. 2020, 04:18 skrev David Schultz <david.schultz@...>:
On 9/25/20 8:46 PM, John Kennedy wrote:
> I unsoldered and replaced D6, D7 and the 74LS10.
> Interestingly the LOW signal at pin 10 of the 74LS10 is exactly as
> expected. However, when the chip is inserted, the logic probe won’t give
> a high or low - there’s a small voltage there. Where could it be coming
> from?

The 47K resistor in the wired-OR is great for CMOS logic but TTL, even
LS TTL, draws more current. A quick check of a data sheet shows input
current  when Vin=0.4V of -0.4mA. Which will create quite the voltage
drop on a 47K resistor.

You could lower that resistance but I can't help but be horrified by the
use of LS TTL with an 1802. 74HC or HCT if you must but please not LS.

David Schultz

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