tepples wrote:
How much more does, say, the Action 53 mapper cost compared to a plain old UOROM (161+32)?
How much does it cost to level-shift each pin?
Action53 multimapper with 512KB of PRG-ROM still fits in a smaller CPLD, so it's more cost effective to still use a smaller 5v-tolerant CPLD. It used 27 macrocells in the XC9536XL. My plan would be to migrate it to use A 32 macrocell lattice M4A3 or isp4000V series CPLD that are close to $1.26 which is comparable to the Xilinx XC9536XL used thus far. So the concerns of level shifting each pin aren't an issue.
The parts cost between a discrete mapper and the CPLD and 3v supply is around $1.50. There is added labors involved with CPLDs compared to discrete mappers though too, but I've tried to keep those minimal for Action53 doing most the work myself.
For a more complex mapper on par with the MMC3/FME7 (effectively something with an IRQ counter and/or fine CHR banking) and beyond that would now make more sense to put in a non-5v tolerant CPLD the cost per level shift would most likely be grouped by 16bits at a time.
FME7, fits perfectly in 16bits, where MMC3 comes goes one bit over with the addition CPU A0
(8) PRG-DATA
(3) PPU A10-12
(3) CPU A0, A13-14
(3) control (PRG R/W PRG /CE M2)
17 bits total.
I'm toying with the idea of using a voltage divider for something like CPU A0, but I'd have to do some thorough testing before that sat well with me. There are smaller options for 4-8bit level shifters, but I'd rather not hassle with them for stocking reasons. EDIT: I guess there are single bit levelshifters under 10cents in qty..
Once pushed to the point of needing two level shifters there are added benefits since you'd get the whole CPU bus down to 3v. Now you're no longer restricted to 5v memories for WRAM/PRG-ROM. So super cheap 4-8MByte 3v TSOP-44 flash becomes attractive if you can stomach the finer pitch that comes with them. That and the cost of 5v sram/flash has been on the rise some of mine have even been EOL recently as well.
The actual cost of level shifters is greatly dependent on quantity purchased, but $0.50/16bits is prob the best number to use I'd say. There are added assembly costs as well to consider.