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