EP80579 Datasheet, PDF (1151/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
31.5.3 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. Both count and status
of the selected counters may be latched simultaneously by setting both bit 5 and bit 4
to 0. If both are latched, the first read operation from that counter returns the latched
status. The next one or two reads, depending on whether the counter is programmed
for one or two byte counts, returns the latched count. Subsequent reads return an
unlatched count.
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 in any or
all of the counters by selecting the counter during the register write. 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 will return 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, return the latched count. Subsequent reads return unlatched count.
Table 31-8. Read Back Command
Bits
07:06
05
04
03
02
01
00
Description
Read Back Command: Must be ‘11’ to select the Read Back Command.
Latch Count of Selected Counters:
0 = Current count value of the selected counters are latched
1 = Current count value of the selected counters are not latched
Latch Status of Selected Counters:
0 = Status of the selected counters are latched
1 = Status of the selected counters are not latched
Counter 2 Select:
0 = Counter 2 count and/or status are not latched
1 = Counter 2 count and/or status are latched
Counter 1 Select:
0 = Counter 1 count and/or status are latched
1 = Counter 1 count and/or status are not latched
Counter 0 Select:
0 = Counter 0 count and/or status are latched.
1 = Counter 0 count and/or status are not latched
Reserved. Must be 0.
§§
August 2009
Order Number: 320066-003US
Intel^® EP80579 Integrated Processor Product Line Datasheet
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