Author Topic: RAM and ROM Routing Nightmare!  (Read 2153 times)

0 Members and 1 Guest are viewing this topic.

Offline David

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
RAM and ROM Routing Nightmare!
« on: July 01, 2010, 10:20:42 am »
Hi all,
I am having a bit of a problem trying to route two IC's together on a new version of my development board. The problem is illustrated in the attached diagram. Basically I cannot get both the Ram and Rom IC's in the same package so the Rom must be a TSOP-I 48 pin while the Ram is a TSOP-II 44 pin. The two ic's must be in the arrangement shown and the address and data bus locations must be in that position. Now the headache comes because both memory devices use the same buses! I have successfully routed the IC's on the first version of my board (show below) but the Ram IC is upside down and obviously looks quite unprofessional! Any ideas?!

In an ideal world the RAM would also be a TSOP-I 48 pin with the same pin-out. Now these devices do (or did...) exist but seem to now be obsolete!

Cheers,
Dave

« Last Edit: July 01, 2010, 10:22:43 am by David »
David
(United Kingdom)
Electronics Design Engineer
 

Offline nessatse

  • Regular Contributor
  • *
  • Posts: 98
  • Country: za
Re: RAM and ROM Routing Nightmare!
« Reply #1 on: July 01, 2010, 11:33:29 am »
On the RAM chip you can pin swap the address and data bits as much as you need to facilitate routing, since the bit numbering is somewhat arbitrary from an external point of view.  Would that help?
 

Offline mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 12124
  • Country: gb
    • Mike's Electric Stuff
Re: RAM and ROM Routing Nightmare!
« Reply #2 on: July 01, 2010, 01:28:53 pm »
On the RAM chip you can pin swap the address and data bits as much as you need to facilitate routing, since the bit numbering is somewhat arbitrary from an external point of view.  Would that help?
You can also do the same for ROM if you shuffle the contents before programming!
This is the sort of layout job where you need to  route the PCB Before comitting pins in the schematic. Some PCB packages allow component pins to be defined as equivalent and it will auto-swap to reduce net length.

Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Offline David

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: RAM and ROM Routing Nightmare!
« Reply #3 on: July 01, 2010, 05:30:33 pm »
After many hours this is what i've come up with so far...needs some refinement but it should work. I know the track lengths are different and will cause timing differences but as the memory won't be accessed at very high speeds I hope this is ok...

Dave

David
(United Kingdom)
Electronics Design Engineer
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf