P ROM: Difference between revisions

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[[File:p_rom.jpg|thumb|right|1MiB P1 ROM]]
[[File:p_rom.jpg|thumb|right|1MiB P1 ROM]]
16bit ROM(s) containing byteswapped [[68k]] binaries in [[cartridges]].
16bit ROM(s) containing the byteswapped [[68k]] program in [[cartridges]].
 
Minimum speed: 150ns. Can use slower ROMs by using the cartridge's wait state configuration.


Sometimes, two 8 bit ROMs are used as a second P ROM (called "SP1/2" or "EP1/2").
Sometimes, two 8 bit ROMs are used as a second P ROM (called "SP1/2" or "EP1/2").


When unbanked, the maximum size is [[68k memory map|1MiB]]. Some games use [[bankswitching]] to use 2MiB or bigger P ROMs.
When not banked, the maximum size is [[68k memory map|1MiB]]. Some games use [[bankswitching]] for larger than 2MiB P ROMs.


Some cartridges use an [[NGPC flash board]] soldered in place of the mask ROMs.
Some cartridges use an [[NGPC flash board]] soldered in place of the mask ROMs.
==Speed==
Minimum speed: 150ns. Can use slower ROMs by using the cartridge's [[wait cycle]] configuration.
==2 MiB P ROMs==
When the P ROM is 2MiB, the second MiB of the P ROM is mapped to $000000->$0FFFFF in the [[68k memory map]], and the first MiB is mapped to $200000->$2FFFFF. In other words, the mebibytes inside the P ROM are swapped when mapped. This is a special case between standard 1MiB P ROMs and larger ROMs that require bankswitching.


[[Category:Chips]]
[[Category:Chips]]
[[Category:Cartridge systems]]
[[Category:Cartridge systems]]

Latest revision as of 18:27, 11 March 2024

File:P rom.jpg
1MiB P1 ROM

16bit ROM(s) containing the byteswapped 68k program in cartridges.

Sometimes, two 8 bit ROMs are used as a second P ROM (called "SP1/2" or "EP1/2").

When not banked, the maximum size is 1MiB. Some games use bankswitching for larger than 2MiB P ROMs.

Some cartridges use an NGPC flash board soldered in place of the mask ROMs.

Speed

Minimum speed: 150ns. Can use slower ROMs by using the cartridge's wait cycle configuration.

2 MiB P ROMs

When the P ROM is 2MiB, the second MiB of the P ROM is mapped to $000000->$0FFFFF in the 68k memory map, and the first MiB is mapped to $200000->$2FFFFF. In other words, the mebibytes inside the P ROM are swapped when mapped. This is a special case between standard 1MiB P ROMs and larger ROMs that require bankswitching.