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B) Stop Frame Timing with Host using 17 IRQSER sampling period
S
R
T
S
IRQSER
PCICLK
Host Controller
IRQ15
Driver
R
T
None
IRQ14
IRQ15
S
R
T
IOCHCK#
None
STOP
R
T
STOP FRAME
H
I
START
NEXT CYCLE
1
2
3
FRAME
H=Host Control
R=Recovery
T=Turn-around
S=Sample
I= Idle.
1)
Stop pulse is 2 clocks wide for Quiet mode, 3 clocks wide for Continuous mode.
2)
There may be none, one or more Idle states during the Stop Frame.
3)
The next IRQSER cycle’s Start Frame pulse may or may not start immediately
after the turn-around clock of the Stop Frame.
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.
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.
Any IRQSER Device (i.e., The FDC37C957) 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.
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.