Shell bottom: No photoScreenshoots: No photoExtra info:
https://forums.nesdev.com/viewtopic.php?f=9&t=13622
Downtown - Nekketsu Monogatari with TTLs!
------------------------------------------------------------------------------------------------
CPU:
$8000-$9fff | $a000-$bfff | $c000-$dfff | $e000-$ffff
$8000 $8002 $8001 -1
------------------------------------------------------------------------------------------------
PPU:
$0000-$03ff|$0400-$07ff|$0800-$0bff|$0c00-$0fff|$1000-$13ff|$1400-$17ff|$1800-$1bff|$1c00-$1fff|
$8010 $8011 $8012 $8013 $8020 $8021 $8022 $8023
------------------------------------------------------------------------------------------------
REGISTERS:
[.... PPPP] $8000/$8001/$8002 (mask $8073): Set PRG bank
||||
++++- PRG bank to set
[.CCC CCCC] $8010/$8011/$8012/$8013/$8020/$8021/$8022/$8023 (mask $8073): Set CHR bank
||| ||||
+++-++++- CHR bank to set
[.... ...E] $8020 (mask: $8070): Counter enable/disable
|
+- 0: disable, 1:enable
[VVVV VVVV] $8030 (mask: $8070): Set counter value
|||| ||||
++++-++++- set low byte of counter to the following value
[VVVV VVVV] $8040 (mask: $8070): Set counter value
|||| ||||
++++-++++- set high byte of counter to the following value
------------------------------------------------------------------------------------------------
Counter operation:
There is 16 bit counter, which counts up and is clocked on every falling edge of M2 (it can be enabled/disabled via $8020)
If it rolls from $ffff to $0000, IRQ is asserted (counter counts from $0000 to $ffff again)
IRQ will be acked automatically after 16 CPU cycles (if counter is still running) or when writing to $8030.