Datasheet

Datasheet 27
Electrical Specifications
3.6 FSB Frequency Select Signals (BSEL[2:0])
The BSEL[2:0] signals are used to select the frequency of the processor input clock
(BCLK[1:0]). These signals should be connected to the clock chip and the appropriate
chipset on the platform. The BSEL encoding for BCLK[1:0] is shown in Table 4.
3.7 FSB Signal Groups
The FSB signals have been combined into groups by buffer type in the following
sections. AGTL+ input signals have differential input buffers that use GTLREF as a
reference level. In this document, the term “AGTL+ Input” refers to the AGTL+ input
group as well as the AGTL+ I/O group when receiving. Similarly, “AGTL+ Output” refers
to the AGTL+ output group as well as the AGTL+ I/O group when driving.
With the implementation of a source-synchronous data bus, two sets of timing
parameters need to be specified. One set is for common clock signals, which are
dependent upon the rising edge of BCLK0 (ADS#, HIT#, HITM#, etc.), and the second
set is for the source-synchronous signals which are relative to their respective strobe
lines (data and address) as well as the rising edge of BCLK0. Asychronous signals are
still present (A20M#, IGNNE#, etc.) and can become active at any time during the
clock cycle. Table 5 identifies which signals are common clock, source synchronous,
and asynchronous.
Table 4. BSEL[2:0] Encoding for BCLK Frequency
BSEL[2] BSEL[1] BSEL[0] BCLK Frequency
L L L 266 MHz
L L H RESERVED
L H H RESERVED
L H L RESERVED
H H L RESERVED
H H H RESERVED
H L H RESERVED
H L L RESERVED