B) Stop Frame Timing with Host using 17 IRQSER sampling period
IRQ14
FRAME
R
IRQ15
FRAME
R
IOCHCK#
FRAME
STOP FRAME
NEXT CYCLE
I 2
S
T
S
T
S
R
T
H
R
T
PCICLK
IRQSER
Driver
1
3
START
STOP
None
IRQ15
None
Host Controller
H=Host Control
R=Recovery
I= Idle.
T=Turn-around
S=Sample
1)
2)
3)
Stop pulse is 2 clocks wide for Quiet mode, 3 clocks wide for Continuous mode.
There may be none, one or more Idle states during the Stop Frame.
The next IRQSER cycle’s Start Frame pulse may or may not start immediately
after the turn-around clock of the Stop Frame.
Any IRQSER Device (i.e., The FDC37B78x)
which detects any transition on an IRQ/Data line
for which it is responsible must initiate a Start
Frame in order to update the Host Controller
unless the IRQSER is already in an IRQSER
Cycle and the IRQ/Data transition can be
delivered in that IRQSER Cycle.
IRQSER Cycle Control
There are two modes of operation for the
IRQSER Start Frame.
1) Quiet (Active) Mode: Any device may initiate
a Start Frame by driving the IRQSER low for one
clock, while the IRQSER is Idle. After driving low
for one clock the IRQSER must immediately be
tri-stated without at any time driving high. A Start
Frame may not be initiated while the IRQSER is
Active. The IRQSER is Idle between Stop and
Start Frames. The IRQSER is Active between
Start and Stop Frames. This mode of operation
allows the IRQSER to be Idle when there are no
IRQ/Data transitions which should be most of the
time.
2) Continuous (Idle) Mode: Only the Host
controller can initiate a Start Frame to update
IRQ/Data line information. All other IRQSER
agents become passive and may not initiate a
Start Frame. IRQSER will be driven low for four
to eight clocks by Host Controller. This mode
has two functions. It can be used to stop or idle
the IRQSER or the Host Controller can operate
IRQSER in a continuous mode by initiating a
Start Frame at the end of every Stop Frame.
Once a Start Frame has been initiated the Host
Controller will take over driving the IRQSER low
in the next clock and will continue driving the
IRQSER low for a programmable period of three
to seven clocks. This makes a total low pulse
width of four to eight clocks. Finally, the Host
Controller will drive the IRQSER back high for
one clock, then tri-state.
An IRQSER mode transition can only occur
during the Stop Frame. Upon reset, IRQSER
bus is defaulted to Continuous mode,
therefore only the Host controller can initiate
the first Start Frame.
Slaves must
continuously sample the Stop Frames pulse
width to determine the next IRQSER Cycle’s
mode.
119
SMSC [ SMSC CORPORATION ]
