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To prevent message coming to the Bus Management host controller from unknown devices in
unknown formats only one method of communication is allowed, a modified form of the Write Word
protocol. The standard Write Word protocol is modified by replacing the command code with the
alerting device's address.
This peripheral supports the Host Notify protocol by setting the BUSEN (I2C_BUSCTL[7]), BMHEN
(I2C_BUSCTL[3]) and ALERTEN (I2C_BUSCTL[4]). In this case the host will acknowledge the Bus
Management Host address (0001 000b). This protocol is used when the device acts as a master
and the host as a slave.
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7
S
SMB Host Addr Wr A
Master (SMBus Device) to Slave
Slave (SMBus Host) to Master
Figure 6.13-19 7-Bit Addressable Device to Host Communication
Bus Management Alert
The Bus Management ALERT optional signal is supported. A slave-only device can signal the host
through the Bus Management ALERT (I2Cn_SMBAL, n=0 or 1) pin that it wants to talk. The host
processes the interrupt and simultaneously accesses all Bus Management ALERT pin's devices
through the Alert Response Address (0001 100b). Only the device(s) which pulled Bus
Management ALERT pin low will acknowledge the Alert Response Address.
When configured as a slave device(BMHEN=0), the Bus Management ALERT pin is pulled low by
setting the ALERTEN bit (I2C_BUSCTL[4]). The Alert Response Address (ARA) is enabled at the
same time.
Figure 6.13-20 7-Bit Addressable Device Responds to an ARA
When configured as a host (BMHEN=1), the ALERT flag (I2C_BUSSTS[3]) is set when a falling
edge is detected on the Bus Management ALERT pin and ALERTEN=1. When ALERTEN=0, the
ALERT line is considered high even if the external Bus Management ALERT pin is low. If the Bus
Management ALERT pin is not needed, the Bus Management ALERT pin can be used as a
standard GPIO if ALERTEN = 0;
Sep 9, 2019
ISD94100 Series Technical Reference Manual
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Device Address
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Page 639 of 928
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Rev1.09
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