Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
991
Clocking and Reset—Intel
®
81341 and 81342
19.1.2
Clocking Region Summary
summarizes all of the input clock pins, output clock pins, and clock strapping
option pins used in 81341 and 81342.
Table 630. Clock Pin Summary (Sheet 1 of 2)
Pin
Input/Output
Description
P_CLKIN
Input
PCI Bus Input Clock:
Provides timing for all PCI transactions
REFCLKP
REFCLKN
Input
PCI Express Input Clock:
Differential 100 MHz Clock
P_M66EN
Input
PCI 66 MHz enable.
TCK
Input
Test Clock:
provides clock input for IEEE 1149.1 Boundary Scan Testing
(JTAG).
HS_FREQ[1:0]
/
CR_FREQ[1:0]
Strap/Output
Hot-Swap
Frequency:
While in Hot-Swap mode (
HS_SM#
= 0 and
PCIX_EP#
= 0), these pins are inputs which determine the PCI bus
mode and frequency. See
Section 19.1.1.2, “Clocking Region 2 (PCI)” on
for more details.
Central Resource Frequency:
While operating in Central Resource
Mode (
PCIX_EP#
= 1), these pins are outputs which control an external
PCI-X clock generator.
P_CLKOUT
Output
PCI Bus Output Clock:
When
REFCLKN
/
REFCLKP
are used, the IO
Processor can generate the PCI output clocks. This pin would then be
connected to
P_CLKIN
and trace length matched to
P_CLKO[3:0]
.
The
P_CLKOUT
and
P_CLKO[3:0]
outputs are enabled when the PCI-X
Interface is operating as a central resource (
PCIX_EP#
= 1) and the
PCI Express* input clock is used as the primary clock input
(
CLK_SRC_PCIE#
= 0). See
Section 19.1.1.2.4, “Secondary Clock
for more details.
P_CLKO[3:0]
Output
PCI Bus Output Clocks:
When
REFCLKN
/
REFCLKP
are used, the I/O
processor can generate the PCI output clocks. These pins then provide
the PCI clocks to devices on the PCI bus.
The
P_CLKOUT
and
P_CLKO[3:0]
outputs are enabled when the PCI-X
Interface is operating as a central resource (
PCIX_EP#
= 1) and the
PCI Express* input clock is used as the primary clock input
(
CLK_SRC_PCIE#
= 0). See
Section 19.1.1.2.4, “Secondary Clock
for more details.
M_CK[2:0]
M_CK#[2:0]
Output
Memory Clocks:
Three differential clock pairs for unbuffered DIMMs for
the external SDRAM memory subsystem. Registered DIMMs only use the
M_CK[0]/M_CK#[0] pair.
CKE[1:0]
Output
SDRAM Clock Enable:
Enables the clocks for the SDRAM memory.
Deasserting places the SDRAM in self-refresh mode.
SCL
[2:0]
Input/Output
I
2
C Clock:
These are bi-directional Open Drain clocks that provides for
synchronous operation of the I
2
C buses.
SMBCLK
Input/Output
SMBus Output Clock:
Bi-directional open-drain clock that provides for
synchronous operation of the SMBus.
CLK_SRC_PCIE#
Strap
Selects the clock source used to drive the internal logic and Intel
XScale
®
processor.
0 = Source clock is the PCI Express* reference clock (
REFCLKN
/
REFCLKP
). Note that if this selection is made, the
REFCLKN
/
REFCLKP
must be provided regardless of the PCI Express interface
mode: Endpoint or Root Complex.
1 = Source clock is the PCI input clock (
P_CLKIN
). Note that if this
selection is made, the
P_CLKIN
must be provided regardless of the
PCI-X interface mode: Endpoint or Central Resource.
Note:
CLK_SRC_PCIE#
is not sampled during a WARM Reset.