MEC1322 Datasheet, PDF (165/456 Pages) Microchip Technology – Keyboard and Embedded Controller for Notebook PC

FIGURE 12-3:
MAILBOX SIRQ AND SMI ROUTING
Mailbox Registers
MBX_Host_SIRQ
MBX_Host_SMI
MEC1322
SIRQ Mapping
SIRQ
GPIO
nSMI
Pin Control Register
12.10.3 EC MAILBOX CONTROL
The HOST-to-EC Mailbox Register and EC-to-Host Mailbox Register are designed to pass commands between the host
and the EC. If enabled, these registers can generate interrupts to both the Host and the EC.
The two registers are not dual-ported, so the HOST BIOS and Keyboard BIOS must be designed to properly share these
registers. When the host performs a write of the HOST-to-EC Mailbox Register, an interrupt will be generated and seen
by the EC if unmasked. When the EC writes FFh to the Mailbox Register, the register resets to 00h, providing a simple
means for the EC to inform the host that an operation has been completed.
When the EC writes the EC-to-Host Mailbox Register, an SMI may be generated and seen by the host if unmasked.
When the Host CPU writes FFh to the register, the register resets to 00h, providing a simple means for the host to inform
that EC that an operation has been completed.
Note:
The protocol used to pass commands back and forth through the Mailbox Registers Interface is left to the
System designer. Microchip can provide an application example of working code in which the host uses the
Mailbox registers to gain access to all of the EC registers.
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DS00001719D-page 165