Search found 26 matches

by doragasu
Mon Apr 11, 2016 11:39 pm
Forum: NES Hardware and Flash Equipment
Topic: What acknowledges MMC3 IRQ?
Replies: 13
Views: 4564

Re: What acknowledges MMC3 IRQ?

Thanks a lot, I think everything is clear now! @byemu: Wow, nice cart! Is your implementation open? It would be nice to browse the HDL sources! About the FPGANES sources you pointed out, I don't know verilog, but I think it's readable enough to understand how it works. BTW, the bankswitching I imple...
by doragasu
Mon Apr 11, 2016 8:44 am
Forum: NES Hardware and Flash Equipment
Topic: What acknowledges MMC3 IRQ?
Replies: 13
Views: 4564

Re: What acknowledges MMC3 IRQ?

Thanks for the replies! Interrupts are only generated when the scanline counter is clocked by PPU A12, so writing to E000 and E001 in quick succession shouldn't generate an IRQ. That makes sense, but reading from the wiki I had the impression that it stayed low (for chips with "normal" behavior): - ...
by doragasu
Mon Apr 11, 2016 7:23 am
Forum: NES Hardware and Flash Equipment
Topic: What acknowledges MMC3 IRQ?
Replies: 13
Views: 4564

What acknowledges MMC3 IRQ?

I want to implement an MMC3 clone based on a CPLD. I'm planning to use a Xilinx CoolRunner 2 CPLD (with transceivers for 5V <--> 3.3V translation). So far I have implemented (but have not yet tested) the bankswitching logic. I was going to implement the scanline counter and IRQ logic, and 2 doubts a...
by doragasu
Fri Nov 13, 2015 12:59 am
Forum: NES Hardware and Flash Equipment
Topic: Will this mapper 113 implementation work?
Replies: 18
Views: 8625

Re: Will this mapper 113 implementation work?

Again thanks for the suggestions! Here are some thoughts based on them: I suppose I do not have to take into consideration the 1 uA maximum input current of the HC parts: during discharge it will make the discharge cycle a tad faster, and that doesn't pose a problem (it would be if the discharge cyc...
by doragasu
Thu Nov 12, 2015 5:44 am
Forum: NES Hardware and Flash Equipment
Topic: Will this mapper 113 implementation work?
Replies: 18
Views: 8625

Re: Will this mapper 113 implementation work?

I have notified that the calculations I made are for discharging through R2 (to ensure the capacitor is discharged if there is a RESET of the console), and the 3,9 us timing is for the charging stage (through R1), ensuring addresses are stable before the CPU starts fetching data. So I have to redo t...
by doragasu
Thu Nov 12, 2015 3:17 am
Forum: NES Hardware and Flash Equipment
Topic: Will this mapper 113 implementation work?
Replies: 18
Views: 8625

Re: Will this mapper 113 implementation work?

Recalculated the capacitor more carefully. Sorry for the photo quality. Vol,max value is 0.1V (was cut on the photo): http://i.imgur.com/tHXUvqd.jpg If my calculations are right, for a 100K resistor, I should use a capacitor lower than 34 pF. I suppose 22 pF should be OK, even taking into account th...
by doragasu
Wed Nov 11, 2015 10:02 am
Forum: NES Hardware and Flash Equipment
Topic: Will this mapper 113 implementation work?
Replies: 18
Views: 8625

Re: Will this mapper 113 implementation work?

Revised schematic, lacking the final RC values: http://i.imgur.com/jNcxIjM.png IIRC, Vc(t) = Vo + (Vinf - Vo) exp(-t/(RC)) So C should be (if I did the maths right, I'm in a hurry right now): C = t/(R*(ln(Vinf - Vo) - ln(Vc(t) - Vo))) Vo is approx 5V (it will be a bit less, I might re-calculate it l...
by doragasu
Wed Nov 11, 2015 9:19 am
Forum: NES Hardware and Flash Equipment
Topic: Will this mapper 113 implementation work?
Replies: 18
Views: 8625

Re: Will this mapper 113 implementation work?

Again, you are absolutely right! I just forgot the 138 has 3 enable pins (two of them active low). Also as your configuration decodes all the signals on the 138, I do not need to wire R/W to the register, so I should be able to use the 273 instead of the 377, to guarantee the register is zeroed on r...
by doragasu
Wed Nov 11, 2015 1:23 am
Forum: NES Hardware and Flash Equipment
Topic: Will this mapper 113 implementation work?
Replies: 18
Views: 8625

Re: Will this mapper 113 implementation work?

Again, thanks a lot! Now that I see it, the mux looks obvious! My boolean algebra is too rust :-P [FACEPALM]. I'll implement this change for sure! /ROMSEL = 1, M2 = 1, A14 = 1, A8 = 1, A13 = 0, R/W = 0 ? that's only four high inputs, that fits in a single 74'138. Maybe I'm just missing something, bu...
by doragasu
Tue Nov 10, 2015 2:48 pm
Forum: NES Hardware and Flash Equipment
Topic: Will this mapper 113 implementation work?
Replies: 18
Views: 8625

Re: Will this mapper 113 implementation work?

Thanks a lot for the suggestions! For the address decoding, I started trying with a 138, but it has 3 address inputs plus the enable line, and I needed 4 addresses plus the enable (A15, A14, A13, A8 and Phi2). Also both 139 blocks are from a single chip, so it's OK anyway. About the other suggestion...
by doragasu
Tue Nov 10, 2015 9:34 am
Forum: NES Hardware and Flash Equipment
Topic: Will this mapper 113 implementation work?
Replies: 18
Views: 8625

Will this mapper 113 implementation work?

I am designing a development NES cart, replicating iNES mapper 113 . I'm using 100% discrete logic (plus the memories and the AVR microcontroller to defeat the CIC). Basically I'm using a 74HC139 for address decoding, a 74HC377 octal register and a 74HC157 multiplexer for mirroring selection. This i...