Differences

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--- ff3:ff3us:doc:snes:register [2019/08/08 02:19]
madsiur [Address Bus B Registers]
+++ ff3:ff3us:doc:snes:register [2019/08/10 03:42] (current)
madsiur [PPU1 Status and Version Number]
@@ Line 69: / Line 69: @@
 |Horizontal Counter Latch  |  [[register#Counter Latch|$213C]]  |  OPHCT  |  dual  |  read  |  any time  |
 |Vertical Counter Latch  |  [[register#Counter Latch|$213D]]  |  OPVCT  |  dual  |  read  |  any time  |
-|PPU Status Register  |  ''$213E''  |  STAT77  |  single  |  read  |  any time  |
+|PPU1 Status and Version Number  |  [[register#PPU1 Status and Version Number|$213E]]  |  STAT77  |  single  |  read  |  any time  |
-|PPU Status Register  |  ''$213F''  |  STAT78  |  single  |  read  |  any time  |
+|PPU2 Status and Version Number  |  [[register#PPU2 Status and Version Number|$213F]]  |  STAT78  |  single  |  read  |  any time  |
 |APU IO Registers  |  ''$2140''  |  APUIO0  |  single  |  both  |  any time  |
 |APU IO Registers  |  ''$2141''  |  APUIO1  |  single  |  both  |  any time  |
@@ Line 814: / Line 814: @@
 [[register#Address Bus B Registers|Back to top]]
+===== Counter Latch =====
+<code>
+$213C r w++++ OPHCT - Horizontal Counter Latch
+$213D r w++++ OPVCT - Vertical Counter Latch
+        uuuuuuux xxxxxxxx
+        uuuuuuu   = unused (PPU2 Open Bus)
+        xxxxxxxxx = Scanline Location
+</code>
+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]]
+===== PPU2 Status and Version Number =====
+<code>
+$213F r b++++ STAT78 - PPU2 Status and Version Number
+        flupvvvv
+        f    = Current Interlace-Frame (0=1st, 1=2nd Frame)
+        l    = H/V-Counter/Lightgun/Joypad2.Pin6 Latch Flag (0=No, 1=New Data Latched)
+        u    = unused
+        p    = Frame Rate (PPU2.Pin30)  (0=NTSC/60Hz, 1=PAL/50Hz)
+        vvvv = PPU2 5C78 Version Number (version 1..3)
+</code>