W83627HF/ F/ HG/ G
8. SERIAL IRQ
W83627HF supports a serial IRQ scheme. This allows a signal line to be used to report the legacy
ISA interrupt rerquests. Because more than one device may need to share the signal serial IRQ signal
line, an open drain signal scheme is used. The clock source is the PCI clock. The serial interrupt is
transfered on the IRQSER signal, one cycle consisting of three frames types: a start frame, several
IRQ/Data frame, and one Stop frame.
8.1
Start Frame
There are two modes of operation for the IRQSER Start frame： Quiet mode and Continuous mode.
In the Quiet mode, the peripheral drives the SERIRQ signal active low for one clock, and then tri-
states it. This brings all the states machines of the peripherals from idle to active states. The host con-
troller will then take over driving IRQSER signal low in the next clock and will continue driving the
IRQSER low for programmable 3 to 7 clock periods. This makes the total number of clocks low for 4 to
8 clock periods. After these clocks, the host controller will drive the IRQSER high for one clock and
then tri-states it.
In the Continuous mode, only the host controller initiates the START frame to update IRQ/Data line in-
formation. The host controller drives the IRQSER signal low for 4 to 8 clock periods. Upon a reset, the
IRQSER signal is defaulted to the Continuous mode for the host controller to initiate the first Start
frame.
8.2
IRQ/Data Frame
Once the start frame has been initiated, all the peripherals must start counting frames based on the
rsing edge of the start pulse. Each IRQ/Data Frame is three clocks: Sample phase, Recovery phase,
and Turn-around phase.
During the Sample phase, the peripheral drives SERIRQ low if the corresponding IRQ is active. If the
corresponding IRQ is inactive, then IRQSER must be left tri-stated. During the Recovery phase, the
peripheral device drives the IRQSER high. During the Turn-around phase, the peripheral device left
the IRQSER tri-stated.
The IRQ/Data Frame has a number of specific order, as shown in Table 8-1.
- 76 -
WINBOND [ WINBOND ]
