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.
IRQSER Cycle Control
There are two modes of operation for the
IRQSER Start Frame.
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
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.
the first Start Frame.
Slaves must
continuously sample the Stop Frames pulse
width to determine the next IRQSER Cycle’s
mode.
IRQSER Data Frame
Once a Start Frame has been initiated, the
FDC37M60x will watch for the rising edge of the
Start Pulse and start counting IRQ/Data Frames
from there. Each IRQ/Data Frame is three
clocks: Sample phase, Recovery phase, and
Turn-around phase. During the Sample phase
the FDC37M60x must drive the IRQSER (SIRQ
pin) low, if and only if, its last detected IRQ/Data
value was low. If its detected IRQ/Data value is
high, IRQSER must be left tri-stated. During the
Recovery phase the FDC37M60x must drive the
SERIRQ high, if and only if, it had driven the
IRQSER low during the previous Sample Phase.
During the Turn-around Phase the FDC37M60x
must tri-state the SERIRQ. The FDC37M60x will
drive the IRQSER line low at the appropriate
sample point if its associated IRQ/Data line is
low, regardless of which device initiated the
Start 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.
Any IRQSER Device (i.e., The FDC37M60x)
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.
The Sample Phase for each IRQ/Data follows
the low to high transition of the Start Frame
pulse by a number of clocks equal to the
IRQ/Data Frame times three, minus one. (e.g.
The IRQ5 Sample clock is the sixth IRQ/Data
Frame, (6 x 3) - 1 = 17th clock after the rising
edge of the Start Pulse.)
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
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