SLUSCC7C July 2016 – June 2018 TPS546C23
The SMBALERT_MASK command can be used to prevent a warning or fault condition from asserting the SMBALERT signal.
The command uses the SMBus Write Word command protocol to overlay a “mask byte” with an associated/designated status register. It uses the SMBus Block Write/Block Read protocol – with a block size = 1, to read the mask settings for any given status register. If the host in the Block_Count field of the Block Write portion sends a block size unequal to 1 the device returns a NACK. The device always returns a Block Count of 1 upon reads of SMBALERT_MASK.
The bits in the mask byte align with the bits in the corresponding status register. For example, if the STATUS_TEMPERATURE command were sent with the mask byte 01000000b, then an Overtemperature Warning condition would be blocked from asserting SMBALERT. Please refer to the PMBus v1.3 specification - section 15.38 (SMBALERT_MASK Command) and the SMBus specification Block Write/Block Read protocol for further details.
There are 19 maskable SMBALERT sources in the TPS546C23. Each of these 19 status conditions has an associated EEPROM backed mask bit. These sources are represnted and identified in the status register command descriptions by a particular status bit denoted as having EEPROM backup (for example a bit access of r/wE). Writes and reads to SMBALERT_MASK command code accepts only the following as valid STATUS_x command codes:
Attempting to write a mask byte for any STATUS_X command code other than this list causes the device to set the cml bit in the STATUS_BYTE and the ivd bit in the STATUS_CML registers, and triggers SMBALERT. Attempting to read a mask byte for any STATUS_x command code other than this list returns 00h for the mask byte. Refer to these individual command descriptions for further details on their specific SMBALERT masking capabilities.
There is 1 unique status bit in the TPS546C23 that warrants special clarification: PGOOD_Z (STATUS_WORD) is maskable as an SMBALERT source through SMBALERT_MASK commands to STATUS_WORD. If the user wants to write, or read, the mask bit for PGOOD_Z, the user must put 79h in the STATUS_x COMMAND_CODE field of the SMBALERT_MASK command. PGOOD_Z SMBALERT_MASK bit default to 1.