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System Management Bus Interface
150
Intel
®
 Itanium
®
 Processor 9300 Series and 9500 Series Datasheet
6.2.3
PIROM and Scratch EEPROM Supported SMBus 
Transactions 
The PIROM responds to two SMBus packet types: Read Byte and Write Byte. However, 
since the PIROM is write-protected, it will acknowledge a Write Byte command but 
ignores the data. The Scratch EEPROM responds to Read Byte and Write Byte 
commands. 
 
illustrates the Read Byte command. 
 
illustrates the 
Write Byte command. 
In the tables, ‘S’ represents the SMBus start bit, ‘P’ represents a stop bit, ‘A’ represents 
an acknowledge (ACK), and ‘///’ represents a negative acknowledge (NACK). The 
shaded bits are transmitted by the PIROM or Scratch EEPROM, and the bits that aren’t 
shaded are transmitted by the SMBus host controller. In the tables, the data addresses 
indicate 8 bits.
The SMBus host controller should transmit 8 bits with the most significant bit indicating 
which section of the EEPROM is to be addressed: the PIROM (MSB = 0) or the Scratch 
EEPROM (MSB = 1).
6.3
Memory Component Addressing
The Intel
®
 Itanium
®
 Processor 9300 Series and Intel
®
 Itanium
®
 Processor 9500 Series 
PIR_A[1:0] pins are used as the memory address selection signals. The processor does 
not specify the value on these pins. It is left to the system architect to set the SMBus 
memory map. If the processor is the only device on the bus, these pins may be tied to 
VSS. PIR_A[2] is tied to VSS internal to the processor. 
 shows the address 
connections within the processor package.
Table 6-2.Read Byte SMBus Packet
S
Slave 
Address
Write
A
Command 
Code
A
S
Slave 
Address
Read
A
Data
///
P
1
7-bits
1
1
8-bits
1
1
7-bits
1
1
8-bits
1
1
Table 6-3.Write Byte SMBus Packet
S
Slave 
Address
Write
A
Command 
Code
A
Data
A
P
1
7-bits
1
1
8-bits
1
8-bits
1
1