Specifications

EISA and ISA Bus Support
14.5 EISA DMA Support
of four different transfer modes: single, block, demand, and cascade. The DMA
controller also offers buffer chaining, auto-initialization, and support for a Ring
buffer Data Structure in memory. Buffer Chaining is not supported in OpenVMS
AXP.
Documentation that describes the DMA channel is available from INTEL.
14.6 EISA I/O Address Map
For a detailed description of the register addresses on the INTEL 82350DT Chip
Set, refer to the INTEL documentation.These registers include all the Interrupt
Controller CSRs, the DMA controller CSRs, and the Interval timer CSRs. Note
all addresses and offsets are hexadecimal unless otherwise specified. EISA I/O
space is slot specific for EISA boards, with address bits <15:12> signifying the slot
number the board is in. Thus each slot has available 12 bits, or 4K, of I/O space
(1000h ). As a side effect of keeping the EISA bus backwards compatible with
the ISA bus, certain ranges of this 4K of I/O space are used only for ISA boards.
These ranges are called "alias" addresses in the documentation. Since the ISA
boards react to any 10 bit address which matches their assigned address, EISA
boards are designed to use only addresses with 0s in bits 8 and 9. ISA boards
react only to addresses with bits <9:8> not equal to 00. Thus, if this restriction is
followed, there will be no conflicts between boards. Address aliases mean that the
two address ranges address the same physical board: 0100 is the same as 0900 if
you use only the first 10 bits. In the following list ‘‘z’’ (the EISA slot number) can
range from 0-F.
• 0000 - 00FF are system board (slot 0) addresses
• 0100 - 03FF are ISA board addresses
• 0400 - 04FF are system board (slot 0) addresses
• 0500 - 07FF are "alias" ISA board addresses
• 0800 - 08FF are system board addresses
• 0900 - 0BFF are ISA alias addresses
• 0C00 - 0CFF are system board addresses
• 0D00 - 0FFF are ISA alias addresses
• z000 - z4FF are slot z EISA board addresses
• z500 - z7FF are slot z ISA board addresses
• z800 - z8FF are slot z EISA board addresses
• z900 - zBFF are ISA alias addresses
• zC00 - zCFF are slot z EISA board addresses
• zD00 - zFFF are ISA alias addresses
The following example using the DEC 2000—Model 300 system clarifies the
"alias" addressing. Lets say that we have a DEC 2000 with an EISA board
plugged into slot 1, and an ISA board in slot 4. Assume the ISA board has been
configured using jumpers to respond to starting I/O port address 03F0 (as is the
floppy on DEC 2000). Referencing addresses z3F0, z7F0, zFF0, where z is 0-6 on
DEC 2000, will access the same register on the floppy. If the EISA board plugged
into slot 1 was designed improperly, and included a register at address z3F0, both
boards would try to respond to a reference to address 13F0.
14–5