Differences

This shows you the differences between two versions of the page.

--- hardware:memorymap [2023/08/24 02:02] – clyde
+++ hardware:memorymap [2025/03/12 17:19] (current) – [System Control Registers] clyde
@@ Line 17: / Line 17: @@
 ===== General Purpose RAM =====
-The lowest 8,196 addresses provide general-purpose data storage. Data stored in this range will only be read and written by the main processor, without side effects.
+The lowest 8,192 addresses provide general-purpose data storage. Data stored in this range will only be read and written by the main processor, without side effects.
 Of special note within this section are the ranges $0000-$00FF, and $0100-$01FF, called the Zero Page and the Stack respectively. Addresses in the Zero Page can be accessed more quickly by special opcodes, and addresses in the stack are used by certain operations such as calling and returning from subroutines.
@@ Line 28: / Line 28: @@
 ^ Addr  ^ Use                                      ^
-| $2000 | Write 1 to reset audio coprocessor       |
-| $2001 | Write 1 to send NMI to audio coprocessor |
 | $2005 | Banking Register                         |
-| $2006 | Audio enable and sample rate             |
 | $2007 | Video/Blitter Flags                      |
-| $2008 | Gamepad 1 (Left port)                    |
-| $2009 | Gamepad 2 (Right port)                   |
 ==== Audio Coprocessor ===
-Addresses $2000, $2001, and $2006 are used for controlling the [[hardware:audio|Audio Coprocessor]].
+Addresses $2000, $2001, and $2006 are used for controlling the [[hardware:audio|Audio Coprocessor]]. The first two are used for triggering the RESET and NMI vectors respectively. The high bit of $2006 enables or disables the ACP. The lower seven bits determine the sample rate of the audio system by way of setting the number of clock cycles between the ACP receiving IRQ events. These are also write-only.
+^ Addr  ^ Use                                      ^
+| $2000 | Write to reset audio coprocessor       |
+| $2001 | Write to send NMI to audio coprocessor |
+| $2006 | Audio enable and sample rate           |
+$2000 and $2001 trigger on any write, regardless of value.
 ==== Banking Register ====
@@ Line 64: / Line 66: @@
 | 00001000 | DMA_COLORFILL_ENABLE | Use solid colors for blits instead of sprites                         |
 | 00010000 | DMA_GCARRY           | Set 0 to repeat 16x16 tiles on blit draws                             |
-| 00100000 | DMA_CPU_TO_VRAM      | 0 means CPU accesses Sprite RAM1 means the CPU access the framebuffer |
+| 00100000 | DMA_CPU_TO_VRAM      | 0 means CPU accesses Sprite RAM, 1 means the CPU access the framebuffer |
 | 01000000 | DMA_IRQ              | Enable IRQ signal when blits finish                                   |
 | 10000000 | DMA_OPAQUE           | Set 1 to disable transparency                                         |
@@ Line 73: / Line 75: @@
 The front [[hardware:gamepads|gamepad ports]] can be read at $2008 and $2009. Writing to these addresses will not do anything.
 A byte read from one of these locations will return 6 binary button states from the respective controller. Consecutive reads to the same port will toggle the "select" line on the controller port, causing the controller to change which six button states are being returned. More on reading gamepads can be found in its own article.
+^ Addr  ^ Use                                      ^
+| $2008 | Gamepad 1 (Left port)                    |
+| $2009 | Gamepad 2 (Right port)                   |
 ===== Versatile Interface Adapter =====
@@ Line 82: / Line 88: @@
 The VIA is used to control the "SPI" pins on the cartridge port as well as the general-purpose IO pins on the rear of the console. More detail is available on the specific VIA article.
+^ Addr  ^ Use                                      ^
+| $2800 | I/O Register B |
+| $2801 | I/O Register A |
+| $2802 | Data Direction Register B |
+| $2803 | Data Direction Register A |
+| $2804 | Timer 1 Low-Order Latches/Counter |
+| $2805 | Timer 1 High-Order Counter |
+| $2806 | Timer 1 Low-Order Latches |
+| $2807 | Timer 1 High-Order Latches |
+| $2808 | Timer 2 Low-Order Latches/Counter |
+| $2809 | Timer 2 High-Order Counter |
+| $280A | Shift Register |
+| $280B | Auxiliary Control Register |
+| $280C | Peripheral Control Register  |
+| $280D | Interrupt Flag Register  |
+| $280E | Interrupt Enable Register |
+| $280F | Same as Reg 1 except no "Handshake" |
+[[https://www.westerndesigncenter.com/wdc/documentation/w65c22.pdf|Manufacturer datasheet for W65C22 VIA]]
 ===== Audio RAM =====