Advanced I/O Controller with Motherboard GLUE Logic
Datasheet
If LPC47M182 detects any transition on an IRQ/Data line for which it is responsible, it initiates 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. Slaves
must continuously sample the Stop Frames pulse width to determine the next SER_IRQ Cycle’s mode.
7.23.3 SER_IRQ Data Frame
Once a Start Frame has been initiated, the LPC47M182 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 LPC47M182 drives 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 is left tri-stated. During the Recovery phase the LPC47M182 drives 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 LPC47M182 tri-states the SER_IRQ. The LPC47M182 drives 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).
SER_IRQ Sampling Periods
SER_IRQ PERIOD
SIGNAL SAMPLED
Not Used
IRQ1
# OF CLOCKS PAST START
1
2
2
5
3
IRQ2
8
4
5
6
7
8
9
10
11
12
13
14
15
16
IRQ3
IRQ4
IRQ5
IRQ6
IRQ7
IRQ8
IRQ9
IRQ10
IRQ11
IRQ12
IRQ13
IRQ14
IRQ15
11
14
17
20
23
26
29
32
35
38
41
44
47
SER_IRQ Period 14 is used to transfer IRQ13. Logical devices FDC, Parallel Port, Serial Port, and Keyboard have
IRQ13 as a choice for their primary interrupt.
Revision 1.8 SMSC/Non-SMSC Register Sets (02-24-05)
116
SMSC LPC47M182
DATASHEET
SMSC [ SMSC CORPORATION ]
