LPC47M112_07 SMSC [SMSC Corporation], LPC47M112_07 Datasheet - Page 103

• Manufacturer Part Number: LPC47M112_07
• Description: Enhanced Super I/O Controller with LPC Interface
• Manufacturer: SMSC [SMSC Corporation]

Enhanced Super I/O Controller with LPC Interface
Datasheet
SER_IRQ Cycle Control
There are two modes of operation for the SER_IRQ Start Frame.
1) Quiet (Active) Mode: Any device may initiate a Start Frame by driving the SER_IRQ low for one clock, while the
SER_IRQ is Idle. After driving low for one clock the SER_IRQ must immediately be tri-stated without at any time
driving high. A Start Frame may not be initiated while the SER_IRQ is Active. The SER_IRQ is Idle between Stop
and Start Frames. The SER_IRQ is Active between Start and Stop Frames. This mode of operation allows the
SER_IRQ 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 SER_IRQ low in the next clock
and will continue driving the SER_IRQ 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 SER_IRQ back high for one clock,
then tri-state.
Any SER_IRQ Device (i.e., The LPC47M112) 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 SER_IRQ is already in an
SER_IRQ Cycle and the IRQ/Data transition can be delivered in that SER_IRQ Cycle.
2) Continuous (Idle) Mode: Only the Host controller can initiate a Start Frame to update IRQ/Data line information.
All other SER_IRQ agents become passive and may not initiate a Start Frame. SER_IRQ 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 SER_IRQ or the Host
Controller can operate SER_IRQ in a continuous mode by initiating a Start Frame at the end of every Stop Frame.
An SER_IRQ mode transition can only occur during the Stop Frame. Upon reset, SER_IRQ bus is defaulted to
Continuous mode, therefore only the Host controller can initiate the first Start Frame.
continuously sample the Stop Frames pulse width to determine the next SER_IRQ Cycle’s mode.
SER_IRQ Data Frame
Once a Start Frame has been initiated, the LPC47M112 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 LPC47M112 must drive the SER_IRQ low, if and only if, its last
detected IRQ/Data value was low. If its detected IRQ/Data value is high, SER_IRQ must be left tri-stated. During the
Recovery phase the LPC47M112 must drive the SER_IRQ high, if and only if, it had driven the SER_IRQ low during
the previous Sample Phase. During the Turn-around Phase the LPC47M112 must tri-state the SER_IRQ. The
LPC47M112 will drive the SER_IRQ line low at the appropriate sample point if its associated IRQ/Data line is low,
regardless of which device initiated the Start Frame.
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).
SMSC DS – LPC47M112
SER_IRQ PERIOD
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
SER_IRQ Sampling Periods
SIGNAL SAMPLED
nIO_SMI/IRQ2
DATASHEET
Not Used
IRQ10
IRQ11
IRQ12
IRQ13
IRQ14
IRQ15
IRQ1
IRQ3
IRQ4
IRQ5
IRQ6
IRQ7
IRQ8
IRQ9
Page 103
# OF CLOCKS PAST START
11
14
17
20
23
26
29
32
35
38
41
44
47
2
5
8
Slaves must
Rev. 02-16-07