Talk:RAMBO-1: Difference between revisions
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(→Alternate IRQ timing: No need of checking the irq_delay.) |
m (Deleted obsoleted IRQ speculation.) |
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As for the 2mb PRG, I'm not sure if the cart actually supports that much ROM, but the PRG registers apparently are 8 bits, and 8kb * $100 = 2048kb = 2mb. --[[User:Drag|Drag]] 03:05, 9 November 2011 (UTC) | As for the 2mb PRG, I'm not sure if the cart actually supports that much ROM, but the PRG registers apparently are 8 bits, and 8kb * $100 = 2048kb = 2mb. --[[User:Drag|Drag]] 03:05, 9 November 2011 (UTC) | ||
== Alternate IRQ timing == | == Alternate IRQ timing == | ||
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writes to $E001: irq_enable=true; IRQ acknowledge by CPU. | writes to $E001: irq_enable=true; IRQ acknowledge by CPU. | ||
When the IRQ is clocked by CPU or scanline modes: | * When the IRQ is clocked by CPU or scanline modes: | ||
If irq_reload == true: | If irq_reload == true: | ||
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If irq_counter == 0 and irq_enable == true | If irq_counter == 0 and irq_enable == true | ||
irq_delay=4 (IRQ will be fired 4 CPU cycles later) | irq_delay=4 (IRQ will be fired 4 CPU cycles later) | ||
--[[User:Zepper|Zepper]] ([[User talk:Zepper|talk]]) 21:16, 6 August 2017 (MDT) | |||
Revision as of 03:16, 7 August 2017
As for the 2mb PRG, I'm not sure if the cart actually supports that much ROM, but the PRG registers apparently are 8 bits, and 8kb * $100 = 2048kb = 2mb. --Drag 03:05, 9 November 2011 (UTC)
Alternate IRQ timing
This is how to get 4 games working: Klax, Skull&Crossbones, Rolling Thunder and Hard Drivin'.
- Address mask: $E001.
writes to $C000: irq_latch=data; writes to $C001: irq_reload=true; irq_mode=data&1; writes to $E000: irq_enable=false; IRQ acknowledge by CPU. writes to $E001: irq_enable=true; IRQ acknowledge by CPU.
- When the IRQ is clocked by CPU or scanline modes:
If irq_reload == true: irq_counter = irq_latch; if(irq_latch != 0) irq_counter |= 1; irq_reload=false; Else if irq_counter == 0: irq_counter = irq_latch; Else irq_counter--; If irq_counter == 0 and irq_enable == true irq_delay=4 (IRQ will be fired 4 CPU cycles later)
