ff3:ff3us:doc:snes:register

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ff3:ff3us:doc:snes:register [2019/08/08 02:39]
madsiur [Address Bus B Registers] 		ff3:ff3us:doc:snes:register [2019/08/08 02:57]
madsiur [PPU1 Status and Version Number]
Line 825: Line 825:
  
 These values are latched by reading $2137 when bit 7 of $4201 is set, or by clearing-and-setting bit 7 of $4201 either by writing $4201 or by pin 6 of Controller Port 2 (the latch occurs on the 1->0 transition). Note that the value read is only 9 bits: bits 1-7 of the high byte are PPU2 Open Bus. Each register keeps seperate track of whether to return the low or high byte. The high/low selector is reset to 'low' when $213F is read (the selector is NOT reset when the counter is latched). H Counter values range from 0 to 339, with 22-277 being visible on the screen. V Counter values range from 0 to 261 in NTSC mode (262 is possible every other frame when interlace is active) and 0 to 311 in PAL mode (312 in interlace?), with 1-224 (or 1-239(?) if overscan is enabled) visible on the screen. These values are latched by reading $2137 when bit 7 of $4201 is set, or by clearing-and-setting bit 7 of $4201 either by writing $4201 or by pin 6 of Controller Port 2 (the latch occurs on the 1->0 transition). Note that the value read is only 9 bits: bits 1-7 of the high byte are PPU2 Open Bus. Each register keeps seperate track of whether to return the low or high byte. The high/low selector is reset to 'low' when $213F is read (the selector is NOT reset when the counter is latched). H Counter values range from 0 to 339, with 22-277 being visible on the screen. V Counter values range from 0 to 261 in NTSC mode (262 is possible every other frame when interlace is active) and 0 to 311 in PAL mode (312 in interlace?), with 1-224 (or 1-239(?) if overscan is enabled) visible on the screen.
 +
 +[[register#Address Bus B Registers|Back to top]]
 +
 +===== PPU1 Status and Version Number =====
 +<code>
 +$213E r b++++ STAT77 - PPU1 Status and Version Number
 +        trmuvvvv
 +        t    = OBJ Time overflow  (0=Okay, 1=More than 8x34 OBJ pixels per scanline)
 +        r    = OBJ Range overflow (0=Okay, 1=More than 32 OBJs per scanline)
 +        m    = Master/Slave Mode (PPU1.Pin25) (0=Normal=Master)
 +        u    = unused
 +        vvvv = PPU1 5C77 Version Number (only version 1 exists)
 +</code>
 +
 +Bit t: If more than 34 sprite-tiles (e.g. a 16x16 sprite has 2 sprite-tiles) were encountered on a single line, this flag will be set. The flag is reset at the end of V-Blank but not during forced blank.
 +
 +Bit r: If more than 32 sprites were encountered on a single line, this flag will be set. The flag is reset at the end of V-Blank but not during forced blank. 
 +
 +Note that the above two flags are set whether or not OBJ are actually enabled at the time (see $212C), at the following times: bit 6 when V=OBJ.YLOC/H=OAM.INDEX*2, bit 7 when V=OBJ.YLOC+1/H=0.
  
 [[register#Address Bus B Registers|Back to top]] [[register#Address Bus B Registers|Back to top]]
  • ff3/ff3us/doc/snes/register.txt
  • Last modified: 5 years ago
  • by madsiur