AMD
P R E L I M I N A R Y
32
Am79C970A
19436A-5
FRAME
CLK
AD
IRDY
TRDY
C/
BE
DEVSEL
STOP
IDSEL
1
2
3
4
5
6
1011
PAR
PAR
PAR
BE
DATA
ADDR
7
Figure 2. Slave Configuration Write
Slave I/O Transfers
After the PCnet-PCI II controller is configured as an I/O
device by setting IOEN (for regular I/O mode) or
MEMEN (for memory mapped I/O mode) in the PCI
Command register, it starts monitoring the PCI bus for
access to its CSR, BCR or EEPROM locations. If config-
ured for regular I/O mode, the PCnet-PCI II controller
will look for an address that falls within its 32 bytes of I/O
address space (starting from the I/O base address). The
PCnet-PCI II controller asserts
DEVSEL
if it detects an
address match and the access is an I/O cycle. If config-
ured for memory mapped I/O mode, the PCnet-PCI II
controller will look for an address that falls within its 32
bytes of memory address space (starting from the mem-
ory mapped I/O base address). The PCnet-PCI II con-
troller asserts
DEVSEL
if it detects an address match
and the access is a memory cycle.
DEVSEL
is asserted
two clock cycles after the host has asserted
FRAME
.
The PCnet-PCI II controller will not assert
DEVSEL
if it
detects an address match, but the PCI command is not
of the correct type. In memory mapped I/O mode, the
PCnet-PCI II controller aliases all accesses to the I/O re-
sources of the command types “Memory Read Multiple”
and “Memory Read Line” to the basic Memory Read
command. All accesses of the type “Memory Write and
Invalidate” are aliased to the basic Memory Write com-
mand. 8-bit, 16-bit and 32-bit non-burst transactions are
supported. The PCnet-PCI II controller decodes only the
upper 30 address lines to determine which I/O resource
is accessed.
The typical number of wait states added to a slave I/O or
memory mapped I/O read or write access on the part of
the PCnet-PCI II controller is 6 to 7 clock cycles,
depending upon the relative phases of the internal
Buffer Management Unit clock and the CLK signal,
since the internal Buffer Management Unit clock is a
divide-by-two version of the CLK signal.
The PCnet-PCI II controller does not support burst
transfers for access to its I/O resources. When the host
keeps
FRAME
asserted for a second data phase,
the PCnet-PCI II controller will disconnect the transfer.
The PCnet-PCI II controller supports fast back-to-back
transactions to different targets. This is indicated by the
Fast Back-To-Back Capable bit (PCI Status register,