Intel 521 Data Sheet - Page 67

Land Listing and Signal Descriptions Table 4-3. Signal Description (Sheet 2 of 8) Name Type Description BINIT# BNR# BOOTSELECT BPM[5:0]# BPRI# BR0# BSEL[2:0] COMP[1:0] Input/ Output BINIT# (Bus Initialization) may be observed and driven by all processor FSB agents and if used, must connect the appropriate pins/lands of all such agents. If the BINIT# driver is enabled during power-on configuration, BINIT# is asserted to signal any bus condition that prevents reliable future operation. If BINIT# observation is enabled during power-on configuration, and BINIT# is sampled asserted, symmetric agents reset their bus LOCK# activity and bus request arbitration state machines. The bus agents do not reset their IOQ and transaction tracking state machines upon observation of BINIT# activation. Once the BINIT# assertion has been observed, the bus agents will re-arbitrate for the FSB and attempt completion of their bus queue and IOQ entries. If BINIT# observation is disabled during power-on configuration, a central agent may handle an assertion of BINIT# as appropriate to the error handling architecture of the system. Input/ Output BNR# (Block Next Request) is used to assert a bus stall by any bus agent unable to accept new bus transactions. During a bus stall, the current bus owner cannot issue any new transactions. Input Input/ Output This input is required to determine whether the processor is installed in a platform that supports the Pentium 4 processor in the 775-land package. The processor will not operate if this signal is low. This input has a weak internal pull-up to VCC. BPM[5:0]# (Breakpoint Monitor) are breakpoint and performance monitor signals. They are outputs from the processor which indicate the status of breakpoints and programmable counters used for monitoring processor performance. BPM[5:0]# should connect the appropriate pins/lands of all processor FSB agents. BPM4# provides PRDY# (Probe Ready) functionality for the TAP port. PRDY# is a processor output used by debug tools to determine processor debug readiness. BPM5# provides PREQ# (Probe Request) functionality for the TAP port. PREQ# is used by debug tools to request debug operation of the processor. These signals do not have on-die termination. Refer to Section 2.5 for termination requirements. Input BPRI# (Bus Priority Request) is used to arbitrate for ownership of the processor FSB. It must connect the appropriate pins/lands of all processor FSB agents. Observing BPRI# active (as asserted by the priority agent) causes all other agents to stop issuing new requests, unless such requests are part of an ongoing locked operation. The priority agent keeps BPRI# asserted until all of its requests are completed, then releases the bus by de-asserting BPRI#. Input/ Output BR0# drives the BREQ0# signal in the system and is used by the processor to request the bus. During power-on configuration this signal is sampled to determine the agent ID = 0. This signal does not have on-die termination and must be terminated. Output The BCLK[1:0] frequency select signals BSEL[2:0] are used to select the processor input clock frequency. Table 2-6 defines the possible combinations of the signals and the frequency associated with each combination. The required frequency is determined by the processor, chipset and clock synthesizer. All agents must operate at the same frequency. For more information about these signals, including termination recommendations refer to Section 2.9. Analog COMP[1:0] must be terminated to VSS on the system board using precision resistors. Datasheet 67