82NM10 Datasheet, PDF (112/671 Pages) Intel Corporation – Intel® NM10 Family Express Chipset

Functional Description
5.8.2.3
Read Back Command
The Read Back command, written to port 43h, latches the count value, programmed
mode, and current states of the OUT pin and Null Count flag of the selected counter or
counters. The value of the counter and its status may then be read by I/O access to the
counter address.
The Read Back command may be used to latch multiple counter outputs at one time.
This single command is functionally equivalent to several counter latch commands, one
for each counter latched. Each counter's latched count is held until it is read or
reprogrammed. Once read, a counter is unlatched. The other counters remain latched
until they are read. If multiple count Read Back commands are issued to the same
counter without reading the count, all but the first are ignored.
The Read Back command may additionally be used to latch status information of
selected counters. The status of a counter is accessed by a read from that counter's
I/O port address. If multiple counter status latch operations are performed without
reading the status, all but the first are ignored.
Both count and status of the selected counters may be latched simultaneously. This is
functionally the same as issuing two consecutive, separate Read Back commands. If
multiple count and/or status Read Back commands are issued to the same counters
without any intervening reads, all but the first are ignored.
If both count and status of a counter are latched, the first read operation from that
counter returns the latched status, regardless of which was latched first. The next one
or two reads, depending on whether the counter is programmed for one or two type
counts, returns the latched count. Subsequent reads return unlatched count.
5.9
8259 Interrupt Controllers (PIC) (D31:F0)
Chipset incorporates the functionality of two 8259 interrupt controllers that provide
system interrupts for the ISA compatible interrupts. These interrupts are: system
timer, keyboard controller, serial ports, parallel ports, floppy disk, IDE, mouse, and
DMA channels. In addition, this interrupt controller can support the PCI based
interrupts, by mapping the PCI interrupt onto the compatible ISA interrupt line. Each
8259 core supports eight interrupts, numbered 0–7. Table 5-41 shows how the cores
are connected.
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Datasheet