SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 142

• Manufacturer Part Number: SCH3112I-NE
• Description: LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
• Manufacturer: SMSC [SMSC Corporation]

Rev 0.2 (09-28-04)
SER_IRQ SAMPLING PERIODS
SER_IRQ PERIOD
1
2
3
4
5
6
7
8
9
10
11
12
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 SCH311X 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
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.
Slaves must 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 SCH311X 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 SCH311X 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 SCH311X 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 SCH311X must tri-state the SER_IRQ. The SCH311X 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 = 17
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.
SIGNAL SAMPLED
Not Used
IRQ1
nIO_SMI/IRQ2
IRQ3
IRQ4
IRQ5
IRQ6
IRQ7
IRQ8
IRQ9
IRQ10
IRQ11
DATASHEET
LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
126
th
clock after the rising edge of the Start Pulse).
# OF CLOCKS PAST START
2
5
8
11
14
17
20
23
26
29
32
35
SMSC SCH311X
Datasheet