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Having constructed dev carts for the SMS using original carts and flash roms , i was hoping to go the whole hog and develop a pcb from scratch.

The basic cart would contain a 29F040 , a 32 (or 64 ?)k SRAM and the relevant paging hardware.

The only real hitch i can see at this early stage is that i would still have to liberate an original sega paging chip from a cart to use in my devcart.

so .. i was wondering .. has anyone ever attepmted to emulate the functions of a paging chip either with a collection of TTL logic or PAL's or possible with a low end CPLD. Id love to write the code in a a microchip PIC beacuse im quite well versed in PIC ASM but i don't think the PIC will be fast enough to keep up with the memory access / page switches.

Ill probably build the Devcart<->LPT interface using a PIC tho so as to speed up the transfer by making the PIC generate all the flash write sequences and the paging routines thus leaving the lpt free to just stream the necessary data back and forth ..

any comments will be greatly appreciated .. tia

Mr S

short answer, yes. but it depends on what you mean by full.

32kB games do not require paging hardware and you can use an existing 32kB or 128kB cart PCB with no mods. this works on all master systems and megadrive converters except for early master systems.

most 128 games only page the 16kB segment in 0x8000 to 0xBFFF, so like Codemaster carts, this can be handled by a single PAL.

if, however you want to emulate full paging with SRAM support then you need mulitple register sets, so perhaps using 373 tristate latches with a PAL conrolling all the logic.

as for using microcontroller, a z80 memcycle is 3 clock cycles, so you may be pushing it alittle, even with quick and efficient code. i'd recommend an ATMEL AVR 8-bit single cycle instruction risc microcontroller available upto 30MHz, over a pathetic PIC.

hope you have PROTEL =o)

a s out.

Author	Message
MrSporty Guest	Emulating a paging chip for a 100% homebrew Devcart Posted: Wed Jan 30, 2002 12:19 pm
MrSporty Guest	Having constructed dev carts for the SMS using original carts and flash roms , i was hoping to go the whole hog and develop a pcb from scratch. The basic cart would contain a 29F040 , a 32 (or 64 ?)k SRAM and the relevant paging hardware. The only real hitch i can see at this early stage is that i would still have to liberate an original sega paging chip from a cart to use in my devcart. so .. i was wondering .. has anyone ever attepmted to emulate the functions of a paging chip either with a collection of TTL logic or PAL's or possible with a low end CPLD. Id love to write the code in a a microchip PIC beacuse im quite well versed in PIC ASM but i don't think the PIC will be fast enough to keep up with the memory access / page switches. Ill probably build the Devcart<->LPT interface using a PIC tho so as to speed up the transfer by making the PIC generate all the flash write sequences and the paging routines thus leaving the lpt free to just stream the necessary data back and forth .. any comments will be greatly appreciated .. tia Mr S

asynchronous Joined: 14 Aug 2000 Posts: 742 Location: Adelaide, Australia	Posted: Fri Feb 01, 2002 2:26 am
	short answer, yes. but it depends on what you mean by full. 32kB games do not require paging hardware and you can use an existing 32kB or 128kB cart PCB with no mods. this works on all master systems and megadrive converters except for early master systems. most 128 games only page the 16kB segment in 0x8000 to 0xBFFF, so like Codemaster carts, this can be handled by a single PAL. if, however you want to emulate full paging with SRAM support then you need mulitple register sets, so perhaps using 373 tristate latches with a PAL conrolling all the logic. as for using microcontroller, a z80 memcycle is 3 clock cycles, so you may be pushing it alittle, even with quick and efficient code. i'd recommend an ATMEL AVR 8-bit single cycle instruction risc microcontroller available upto 30MHz, over a pathetic PIC. hope you have PROTEL =o) a s out.

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