Datasheet 33
Electrical Specifications
Listed in Table2-25 are the system bus ratios defined for the Itanium 2 processor. The Itanium 2
processor supports bus ratios of 2/9, 2/10, 2/13, 2/14, 2/15 and 2/16. Table 2-25 lists the system bus
ratios defined for the Itanium 2 processor. Each particular implementation of the Itanium 2
processor only supports a small subset of the ratios listed in Table 2 -25. The supported ratios are
defined below:
•The Itanium 2 processor 900 MHz with 1.5 MB L3 cache supports a bus ratio of 2/9.
•The Itanium 2 processor 1.0 GHz with 3 MB L3 cache supports a bus ratio of 2/10.
•The Itanium 2 processor 1.30 GHz with 3 MB L3 cache supports a bus ratio of 2/13.
•The Itanium 2 processor 1.40 GHz with 4 MB L3 cache supports a bus ratio of 2/14.
•The Itanium 2 processor 1.50 GHz with 6 MB L3 cache supports a bus ratio of 2/15.
•All other Itanium 2 processors will be locked at the correct supported ratios.
The Itanium 2 processor bus to core ratio is configured during system reset by using the A[21:17]#
signal pins. These bus ratio configuration pins are required to be stable and valid during the
duration of the reset sequence as defined below.
Cold Reset Sequence:
•The bus ratio configuration pins (A[21:17]#) must be asserted the entire time RESET# is
asserted.
•RESET# must be asserted before PWRGOOD is asserted.
•The duration from the assertion of PWRGOOD to the deassertion of RESET# must be 1
millisecond minimum.
•After RESET# is deasserted, all the configuration, including the bus ratio configuration pins
A[21:17]#, must remain valid for 2 BCLKs (minimum) to 3 BCLKs (maximum).
•BCLK is shown as a time reference to the BCLK period. It is not a requirement that this is
BCLKn or BCLKp signal.
•Configuration signals other than A[21:17]# must be asserted 4 BCLKs prior to the deasserted
edge of RESET# and must remain valid for 2 BCLKs (minimum) to 3 BCLKs (maximum)
after the deasserted edge of RESET#.
Figure 2-6 outlines the timing relationship between the bus ratio configuration pins, RESET# and
PWRGOOD for cold reset.
Table 2-25. Itanium® 2 Processor System Bus Ratios
Core Frequency Ratio of Bus Frequency
to Processor Frequency A21# A20# A19# A18# A17#
900 MHz 2/9 1(L) 0(H) 1(L) 1(L) 0(H)
1.0 GHz 2/10 1(L) 0(H) 1(L) 0(H) 1(L)
1.3 GHz 2/13 1(L) 0(H) 0(H) 1(L) 0(H)
1.4 GHz 2/14 1(L) 0(H) 0(H) 0(H) 1(L)
1.5 GHz 2/15 1(L) 0(H) 0(H) 0(H) 0(H)
Reserved1
NOTES:
1. Reserved bus ratio encodings should never be driven on the bus during reset, otherwise it may cause damage to the
processor.
All other possible encodings