The VIDOMAX_L command together with the bit[0] in (BDh) EXT_CAPABILITY_VIDOMAX_H forms a 9-bit register to set the maximum value of (VID+Offset) allowed via SVID. Setting the 9-bit VIDo_MAX register to 17E (hex) value reaches the maximum possible (VID+Offset) value with 8-bit register for each (VID unsigned, offset signed).

Exceeding VIDo_MAX with (VID + offset) causes a REJ (Reject) response for individual rail SVID requests and a NACK response for all-call SVID requests.

When a write to this register is attempted, the VIDOMAX_L value combined with VIDo_MAX[8] value (bit[0] in (BDh) EXT_CAPABILITY_VIDOMAX_H register) must satisfy a range check:

• If the combined value is not greater than 0, the write is NACKed.
• If the combined value is greater than 0, then the write is ACKed.

Further, VIDo_MAX bit in (BDh) EXT_CAPABILITY_VIDOMAX_H register does not take effect when updated. It only takes effect when the VIDOMAX_L register is written with a value (can be the same value as the current one) and also the combined value satisfies the range check. When attempting to write a new VIDo_MAX value, it is recommended to write in the following order: write into the (BDh) EXT_CAPABILITY_VIDOMAX_H register first, and then write into the VIDOMAX_L register. To illustrate, a few examples are listed below:

• Example #1: Firstly, a value is written into (BDh) EXT_CAPABILITY_VIDOMAX_H register and is acknowledged. Secondly, another write command is sent to (BEh) VIDOMAX_L register and this write is acknowledged too.
  • Result: The 9-bit VIDo_MAX register is updated and takes effect.
• Example #2: A value is written into (BEh) VIDOMAX_L register and is acknowledged. No write command is sent to (BDh) EXT_CAPABILITY_VIDOMAX_H register.
  • Result: The 9-bit VIDo_MAX register is updated in the lower 8-bit (in (BEh) VIDOMAX_L register) and the new value takes effect.
• Example #3: Firstly, a value is written into (BEh) VIDOMAX_L register and is acknowledged. Secondly, another write command is sent to (BDh) EXT_CAPABILITY_VIDOMAX_H register to update VIDo_MAX bit with a new value and this write is acknowledged too.
  • Result: The 9-bit VIDo_MAX register is updated but the VIDo_MAX bit in (BDh) EXT_CAPABILITY_VIDOMAX_H register does not take effect.

Note: (BDh) EXT_CAPABILITY_VIDOMAX_H and (BEh) VIDOMAX_L registers acknowledges a write only when the power conversion is disabled. A write is not allowed (NACK response) when the power conversion is enabled.

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