Revision 1.02 – June 27, 2006
S5935 – PCI Product
Data Book
Target Disconnects
clock but does not complete the data transfer until
IRDY# is asserted. This situation can only occur when
the S5935 is a target. When the S5935 is an initiator,
IRDY# is always asserted during the data phase (no
initiator wait states). The timing diagram in Figure 10b
applies to the S5935 as either a target disconnecting
or an initiator with its target performing a disconnect.
The S5935 performs a target disconnect if a burst
access is attempted to the PCI Operation Registers.
There are many situations where a target may discon-
nect. Slow responding targets may disconnect to
permit more efficient (faster) devices to be accessed
while they prepare for the next data phase, or a target
may disconnect if it recognizes that the next data
phase in a burst transfer is out of its address range. A
target disconnects by asserting STOP#, TRDY#, and
DEVSEL# as shown in Figures 10a and 10b. The initi-
ator in Figure 10a responds to the disconnect
condition by deasserting FRAME# on the following
Figure 55. Target Disconnect Example 1 (IRDY# deasserted)
3
2
1
PCI CLOCK
FRAME #
IRDY#
(I)
(I)
(T)
(T)
TRDY#
STOP#
(T)
DEVSEL#
(I) = DRIVEN BY INITIATOR
(T) = DRIVEN BY TARGET
DATA
TRANSFERRED
TARGET DISCONNECT
IDENTIFIED
Figure 10b. Target Disconnect Example 2 (IRDY# asserted)
2
3
1
PCI CLOCK
FRAME #
IRDY#
(I)
(I)
(T)
(T)
TRDY#
STOP#
(T)
DEVSEL#
(I) = DRIVEN BY INITIATOR
(T) = DRIVEN BY TARGET
DATA
TARGET DISCONNECT
TRANSFERRED SIGNALED, DATA TRANSFERRED
108
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