David let me know if I need to update the site about this mod. John
From: [email protected] [mailto:[email protected]] On Behalf Of Philippe Elie Sent: Sunday, October 12, 2014 4:08 AM To: [email protected] Subject: [N8VEM-S100:5375] Z80 CPU board - D2/D3 port timing problem hi folks, I finally identified the issued that made some CPM (non banked version) hang the system : the RAM bank switching system had a timing issue. More specifically, when the monitor initializes the D2/D3 ports (with 00 and 04 respectively) the second IO access was actually trigerring also a 04 write into the D2 port. I solved the issue by replacing U25 74LS04 by a 74F04 but a little glitch on D2 port enable still appears that makes me a bit concern about the reliability : <https://lh4.googleusercontent.com/-c8bEDnJl8u0/VDpcsyQu39I/AAAAAAAAANY/Zt15ihLoU_g/s1600/Z80%2BD2%2Btiming.jpg> I was wondering whether the problem would come from sOUT : for U39 I used a 74LS08 instead of a 74S08 thinking speeds would be the same and considering the CPU operates at 4Mhz ? Do you that would fix the problem ? thanks in advance for your feedback Philippe -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
