SMBus Quick Start Guide - Freescale Semiconductor

SMBus Quick Start Guide, Rev. 1
MC9S08MP12/16 introduction
ACK and NACK usage:
• I 2 C devices allow the slave not to ACK its slave address, but SMBus requires it to always ACK it
as a mechanism to detect a detachable device’s presence on the bus (battery, docking station, and
so on).
• I 2 C uses NACK to indicate that it cannot receive any more data bytes after it acknowledges its
slave address. SMBus uses NACK to indicate the reception of an invalid command or data.
Protocol:
• SMBus specifies the protocols that a device is allowed to use when communicating with other
SMBus devices on the bus.
Electrical:
The following table lists the main DC parameter differences between I 2 C and SMBus.
V IL
V IH
Table 5. DC parameter comparison between standard I 2 C, fast I 2 C, and SMBus devices 1
Symbol Parameter
Fixed input
level
V DD related
input level
Fixed input
level
V DD related
input level
Std. I 2 C mode device Fast I 2 C mode device SMBUs device
Min Max Min Max Min Max
–0.5 1.5 –0.5 1.5 — 0.8 V
–0.5 0.3V DD –0.5 0.3V DD N/A N/A V
3.0 V DDmax +
0.5
0.7V DD
V DD max +
0.5
1 Source: System Management Bus Specification, version 2.0, Table 10
3.0 V DDmax +
0.5
0.7V DD
10 MC9S08MP12/16 introduction
V DD max +
0.5
The MC9S08MP16 and MC9S08MP12 are members of the low-cost, high-performance HCS08 family of
8-bit microcontrollers (MCUs) from Freescale. All MCUs in the family use the enhanced HCS08 core and
are available with a variety of peripheral modules, memory sizes, memory types, and package types.
MC9S08MP16 supports SMBus version 2.0 with the help of the I 2 C peripheral modules. The following
table summarizes the feature set available in the MC9S08MP16 series MCUs.
Freescale Semiconductor 13
Units
2.1 5.5 V
N/A N/A V
V HYS V IH –V IL N/A N/A 0.05V DD — N/A N/A V
V OL V OL @ 3mA 0 0.4 0 0.4 N/A N/A V
V OL @ 6mA N/A N/A 0 0.6 N/A N/A V
V OL @ 350µA N/A N/A N/A N/A — 0.4 V
I PULLUP N/A N/A N/A N/A 100 350 µA
I LEAK –10 10 –10 10 –5 5 µA