9 replies to this topic

[GadgetUK]

Hi,

Ive been playing around burning my own prototypes - using AMD 27c020 EPROMs.  This has worked fine but I also wanted to burn some 128K images using 27c010 chips.  What makes the Pasiu PCB hard wired to work with the 020's?

Do I need to pull an address line high or low somewhere, or swap some pins around due to the way it uses counters?  Ive read up a bit on it but I still dont get it...

[sage]

depends strongly on how you prepare your prototypes. if you use BLL type, most likely no problem. if they look (by chance) like 128kb commerical Roms, prolem.

Just check the pin layout of the chips.
if the pin which is not used in the 010 but in 020 is _not_ the highest adress pin, but the highest counter you can use roms with same blocksize but only 128 blocks.
it is is the highest adress pin, you can use the full counter but only half the blcok size.
but its unlikely that it is wired like that, because you would have to reoganize the ROM prior to burning.

but you can still burn your 128kb rom into a 256kb rom. or why do you think most of the rom copies in internet exist in a 256k version even s only 128k are used

[GadgetUK]

Does the Lynx detect usage of pins A9 and A10, A9 seems to be used for cart size > 128K, and A10 for cart size > 256K.  

Its starting to sink in now but unsure how the Lynx knows to treat the card as 128K, 256K, or 512K....

Ive just thought about it again now and wondering if A12 is the answer.... 512 byte blocks for 128K, 1024 byte blocks for 256K, and 2048 byte blocks for 512K...  A12 operates the same for any of the 3 EPROM sizes, it just increases sector size.  

My head is telling me that despite all of the above, a card wired for a 27c020, will map a 27c010 correctly as theres one less address line and its just the byte layout on the cart thats the problem - or am I wrong?

[sage]

GadgetUK, on Sat Aug 4, 2012 5:30 PM, said:

Its starting to sink in now but unsure how the Lynx knows to treat the card as 128K, 256K, or 512K....

Not at all. There is no way to detect the layout automatically.(*)
The layout has to be known to the "software".
If you have a ROM with 128 blocks and blocksize 1k the layout will differ from 256 blocks and 512 bytes blocksize even so the final size is the same.

GadgetUK, on Sat Aug 4, 2012 5:30 PM, said:

Does the Lynx detect usage of pins A9 and A10, A9 seems to be used for cart size > 128K, and A10 for cart size > 256K.  

no. seen above.

GadgetUK, on Sat Aug 4, 2012 5:30 PM, said:

Ive just thought about it again now and wondering if A12 is the answer.... 512 byte blocks for 128K, 1024 byte blocks for 256K, and 2048 byte blocks for 512K...  A12 operates the same for any of the 3 EPROM sizes, it just increases sector size.  

no. seen above.

GadgetUK, on Sat Aug 4, 2012 5:30 PM, said:

My head is telling me that despite all of the above, a card wired for a 27c020, will map a 27c010 correctly as theres one less address line and its just the byte layout on the cart thats the problem - or am I wrong?

again. it depends if you keep the blocksize constant.

(*)
actually, the rom layout can be detected by reading the amximum blocksize and then detect doubled data which tell you which lines are not used.
same can be archieved to detect if you have 64, 128 and 256 blocks.

Maybe you should search the forum, i think we had this discussions here already.

[GadgetUK]

I have, and found some good info from Karri, but still unclear.  Ive made some pin mappings for each of the cart sizes.  Ive not checked yet but if the 256K has at least the 128K address lines all mapped, in theory a 128K image could be re-ordered to work on the pasiu board - but ive not checked yet since I did the pin mappings last night.  The other thing ive started is a lynx to dip32 adaptor so I can backup zaku and a few other roms and use on my gp2x

[sage]

GadgetUK, on Mon Aug 6, 2012 1:42 PM, said:

I have, and found some good info from Karri, but still unclear.  Ive made some pin mappings for each of the cart sizes.  Ive not checked yet but if the 256K has at least the 128K address lines all mapped, in theory a 128K image could be re-ordered to work on the pasiu board - but ive not checked yet since I did the pin mappings last night.  The other thing ive started is a lynx to dip32 adaptor so I can backup zaku and a few other roms and use on my gp2x

Tse tse tse.
Its so much easier just to transmit teh ROM content by Comlynx

[sage]

GadgetUK, on Mon Aug 6, 2012 1:42 PM, said:

Ive made some pin mappings for each of the cart sizes.  Ive not checked yet but if the 256K has at least the 128K address lines all mapped, in theory a 128K image could be re-ordered to work on the pasiu board - but ive not checked yet since I did the pin mappings last night.

Again, you can alsways burn a 128k ROM into a 256kb ROM by just doubling each block of  data (in case of epyx ROM) or by just doubling the full content (in case of BLL rom)

[GadgetUK]

sage, on Mon Aug 6, 2012 3:07 PM, said:

GadgetUK, on Mon Aug 6, 2012 1:42 PM, said:

I have, and found some good info from Karri, but still unclear.  Ive made some pin mappings for each of the cart sizes.  Ive not checked yet but if the 256K has at least the 128K address lines all mapped, in theory a 128K image could be re-ordered to work on the pasiu board - but ive not checked yet since I did the pin mappings last night.  The other thing ive started is a lynx to dip32 adaptor so I can backup zaku and a few other roms and use on my gp2x

Tse tse tse.
Its so much easier just to transmit teh ROM content by Comlynx

Really?? How, presumably I would need to make a serial adapter to comlynx, and boot some cart that provides interface, and I would need to open lynx and join the cart detect pins wouldnt I, so I can swap the cart without reboot?  Sounds easier to make an adapter for eeprom.. Ive got a failed lynx 2 PCB so taking the card socket and mapping to a DIP32 just needs some wire and patience.

[GadgetUK]

Thanks for the help on this btw =)

[GadgetUK]

For anyone finding this thread in future, I wrote the exe in this other thread to easily convert a 128K image for use in a 256K chip via the Pasiu PCB.

http://www.atariage....k/#entry2581038