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Reference Data 111
I/O map
The following table gives descriptions of what the memory is used for at
each address location.
Address
(hex)
Size Description
0000–000F 16 bytes DMA-1
0020–0021 2 bytes INT-1
0040 1 byte Programmable interval timer 1
0041 1 byte Refresh request counter 1
0042 1 byte Speaker tone counter 2
0043 1 byte Command mode register
0048 1 byte Programmable interval timer 2
0049 1 byte Reserved
004A 1 byte CPU speed control counter 2
004B 1 byte Command mode register
0061-0070 16 bytes NMI status/registers
0080-008F 16 bytes DMA page registers
00A0-00A1 2 bytes INT-2
00C0-00DE 31 bytes DMA2
0400-040F 16 bytes DMA1
0461-0464 4 bytes Extended NMI control
0480-048F 16 bytes DMA high page register
04C2 1 byte Reserved
04C6-04CE 8 bytes DMA2
04D0-04DF 16 bytes INT/DMA2
04E0-04FF 32 bytes DMA
4075.book Page 111 Friday, April 2, 1999 9:26 AM