PORTIBM PC Portable (uses same BIOS as XT) 00C0-00DF - DMAsee Direct Memory Access 2 - SECOND DIRECT MEMORY ACCESS CONTROLLER (8237)

00C0  RW  DMAsee Direct Memory Access channel 4 memory address bytes 1 and 0 (low) (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00C2  RW  DMAsee Direct Memory Access channel 4 transfer count bytes 1 and 0 (low) (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00C4  RW  DMAsee Direct Memory Access channel 5 memory address bytes 1 and 0 (low) (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00C6  RW  DMAsee Direct Memory Access channel 5 transfer count bytes 1 and 0 (low) (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00C8  RW  DMAsee Direct Memory Access channel 6 memory address bytes 1 and 0 (low) (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00CA  RW  DMAsee Direct Memory Access channel 6 transfer count bytes 1 and 0 (low) (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00CC  RW  DMAsee Direct Memory Access channel 7 memory address byte 0 (low), then 1 (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00CE  RW  DMAsee Direct Memory Access channel 7 transfer count byte 0 (low), then 1 (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)

00D0  R-  DMAsee Direct Memory Access channel 4-7 status register (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).) (see #P0481)
00D0  -W  DMAsee Direct Memory Access channel 4-7 command register (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).) (see #P0482)
00D2  -W  DMAsee Direct Memory Access channel 4-7 write request register (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00D4  -W  DMAsee Direct Memory Access channel 4-7 write single mask register (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).) (see #P0484)
00D6  -W  DMAsee Direct Memory Access channel 4-7 mode register (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).) (see #P0485)
00D8  -W  DMAsee Direct Memory Access channel 4-7 clear byte pointer flip-flop (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)

00DA  R-  DMAsee Direct Memory Access channel 4-7 read temporary register (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00DA  -W  DMAsee Direct Memory Access channel 4-7 master clear (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00DC  -W  DMAsee Direct Memory Access channel 4-7 clear mask register (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).)
00DE  -W  DMAsee Direct Memory Access channel 4-7 write mask register (ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT.  See also EISA., EISA(Enhanced Industry-Standard Architecture) A 32-bit superset of the IBMInternational Busiuness Machines ATIBM PC AT's expansion bus (which is now known as the ISA or Industry-Standard Architecture bus).) (see #P0486)
Notes:	the temporary register is used as holding register in memory-to-memory
	  DMAsee Direct Memory Access transfers; it holds the last transferred byte
	channel 4 is used for cascading the first (8-bit) DMAsee Direct Memory Access controller
	base/current address registers can only address the memory in 16-bit
	  words (i.e. they contain lines A1-A16 of the address bus with line
	  A0 always equal to 0); base/current word count registers contain the
	  number of 16-bit words
	command and request registers do not exist on PS/2IBM PS/2, any model DMAsee Direct Memory Access controller


Bitfields for DMAsee Direct Memory Access channel 4-7 status register:
Bit(s)	Description	(Table P0481)
 7 = 1	channel 7 request
 6 = 1	channel 6 request
 5 = 1	channel 5 request
 4 = 1	channel 4 request
 3 = 1	terminal count on channel 7
 2 = 1	terminal count on channel 6
 1 = 1	terminal count on channel 5
 0 = 1	terminal count on channel 4
SeeAlso: #P0001,#P0482


Bitfields for DMAsee Direct Memory Access channel 4-7 command register:
Bit(s)	Description	(Table P0482)
 7	DACK sense active high
 6	DREQ sense active high
 5	=1  extended write selection
	=0  late write selection
 4	rotating priority instead of fixed priority
 3	compressed timing
 2	=1  enable controller
	=0  enable memory-to-memory transfer
 1-0	channel number (00 = 4 to 11 = 7)
SeeAlso: #P0002,#P0481,#P0484


Bitfields for DMAsee Direct Memory Access channel 4-7 request register:
Bit(s)	Description	(Table P0483)
 7-3	reserved (0)
 2	=0 clear request bit
	=1 set request bit
 1-0	channel number
	00 channel 4 select
	01 channel 5 select
	10 channel 6 select
	11 channel 7 select
SeeAlso: #P0003,#P0484


Bitfields for DMAsee Direct Memory Access channel 4-7 write single mask register:
Bit(s)	Description	(Table P0484)
 7-3	reserved
 2	=0  clear mask bit
	=1  set mask bit
 1-0	channel select
	00 channel 4 select
	01 channel 5 select
	10 channel 6 select
	11 channel 7 select
SeeAlso: #P0004,#P0482


Bitfields for DMAsee Direct Memory Access channel 4-7 mode register:
Bit(s)	Description	(Table P0485)
 7-6	transfer mode
	00  demand mode
	01  single mode
	10  block mode
	11  cascade mode
 5	direction
	0  address increment select
	1  address decrement select
 4	autoinitialisation enabled
 3-2	operation
	00  verify operation
	01  write to memory
	10  read from memory
	11  reserved
 1-0	channel number
	00  channel 4 select
	01  channel 5 select
	10  channel 6 select
	11  channel 7 select
SeeAlso: #P0005,#P0484


Bitfields for DMAsee Direct Memory Access channel 4-7 write mask register:
Bit(s)	Description	(Table P0486)
 7-4	reserved
 3	channel 7 mask bit
 2	channel 6 mask bit
 1	channel 5 mask bit
 0	channel 4 mask bit
Note:	each mask bit is automatically set when the corresponding channel
	  reaches terminal count or an extenal EOP sigmal is received
SeeAlso: #P0484,#P0006