# HG changeset patch
# User Michael Pavone <pavone@retrodev.com>
# Date 1458921989 25200
# Node ID 08b69e3f9f177496547dc00e19b5add291159b74
# Parent  6204c81e29334720340227a8a46957101eb94395
Fleshed out the video hardware design somewhat

diff -r 6204c81e2933 -r 08b69e3f9f17 simple_console.txt
--- a/simple_console.txt	Wed Mar 23 19:19:29 2016 -0700
+++ b/simple_console.txt	Fri Mar 25 09:06:29 2016 -0700
@@ -83,6 +83,12 @@
 r14 : PC
 r15 : status register
 
+Special Registers
+epc - Exception PC - Stores PC value to resume to when entering an exception handler
+esr - Exception SR - same as above, but for SR
+eur - Exceptuion User Reg - reg for temporary storage of a reg in a handler, intended to be used for the stack pointer
+enum - Exception Number - holds the number of the most recent exception
+
 IO: Ports
 
 0: Controller 1
@@ -105,11 +111,87 @@
 A: Timer Freq
 B: "Serial" Debug Port
 
-D: Write Pallette Address : Read Vertical Position
-E: Write Name Table Address : Read Horizontal Position
-F: Write Sprite Table Address : Read Status?
+C: Write Vertical Scroll : Read Vertical Position
+	MMMM MCCC CCCC CFFF
+	C = coarse scroll bit
+	F = fine scroll bit
+	M = mask bit
+		controls which bits come directly from register
+		and which bits come from the sum of the register
+		and the current line number
+		
+D: Write Horizontal Scroll : Read Horizontal Position
+	xxxx xxxC CCCC CFFF
+	C = coarse scroll bit
+	F = fine scroll bit
+	x = unused
+E: Write Dest Address : Read Status
+F: Write Data : Read Data
+
+
+Name Table Start Address:
+	0VVV VVVV VHHH HHH0
+	
+	V = Coarse scroll bit from vertical scroll value
+	H = Coarse scroll bit from horizontal scroll value
+	
+VDP Memory Map
+0000 - 7FFF = Pattern/Name Table RAM
+8000 - FDFF = unused, returns $FFFF
+FE00 - FEFF = Sprite RAM
+FF00 - FF7F = Palette RAM
+FF80 - FFFF = Palette RAM (mirror)
+
+Another View -
+	MSB determines whether destination is main RAM
+	For MSB 1
+		Next 7 MSB determines which special RAM is the destination
+		Only values of 7E and 7F are valid for these bits at present
+		8 LSB determine offset (1 LSB ignored)
+		
+Writing to Data port puts word into FIFO
+Offset within memory type is increment when word is pulled from FIFO
+
+Pattern Format:
+4bpp in an 8x8 tile arrangement
+
+
+Sprite Table Entry:
+
+XXXXXXXX YYYYYYYY
+IXPVHSNN NNNNNNNN
+
+S: size -- 0 = 8x8, 1 = 16x16
+P: Palette selector
+H: Horizontal flip
+V: Vertical flip
+I: Priority
+N: Name
+X: X position (left of screen = 16, right of screen = ?)
+Y: Y position (top of screen = 16, bottom of screen = 240)
+
+
+Name Table Entry:
+
+IPPVHxNN NNNNNNNN
+
+P: Palette selector
+H: Horizontal flip
+V: Vertical flip
+I: Priority
+N: Name
+x: Unused, should be set to 0
+
+26.112 MHZ Clock
+Dot Clock Divider 4
+CPU Clock Divider 20 (assuming 1 cycle/instruction, 5 for 4 cycles/instruction)
+Audio Timer Divider 34
+Audio Output Divider 544
+
+Alternatively 13.056 Mhz clock and cut the dividers in half
 
 
 
-
-
+H-Counter goes from 0-415 and then wraps back to zero
+V-Counter goes from 0-261 and then wraps back to zero
+V-Counter increments when H-Counter wraps