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OCPRF100 MP Server System Technical Product Specification
Revision 1.0
128
10.2.10.5 ICMB Transmit Control
The FPC’s TXD (transmitted) pin drives both the COM2’s SOUT_TTL_COM2 signal and the
ICMB’s SOUT_TTL_ICMB signal. There is no interlock for preventing the FPC from simulta-
neously transmitting on both ICMB and COM2; in fact, this capability could be desirable.
The FPC drives the ICMB bus with the FPC’s TXD output whenever the ICMB_EN_LATCH is
asserted (high).
10.2.10.6 COM2 Transmit Control
The COM2 transmit signals are connected to either the FPC or the SMC Super I/O* (SIO) chip
depending on the states of the COM2 signals. Note that this discussion is limited solely to the
TXD signals since this is the only signal that the FPC can control.
The routing of COM2 to the SMC I/O chip or FPC and the routing of the ICMB to the FPC is con-
trolled by two signals, COM2_TO_FP_EN_L and COM2_TO_SIO_EN. Note that if these two sig-
nals are not carefully controlled by firmware, the VCC_BACKUP can be shorted to ground. The
VCC_BACKUP is shorted to ground via the SIO’s power pins. In this case, the power supplies
will cycle the entire system and component damage may occur. When switching between
enabling of these routings, it is important never to enable both these signals at the same
time.
Table 10-7: Allowed Combination of States shows the allowed combination of states.
† ICMB available means that if the ICMB_SOUT_EN signal is asserted then the FPC will transmit to the ICMB bus.
The data that is transmitted comes from the microcontroller’s TXD output pin. Note that this capability is independent of
the states of the COM2_TO_SIO_EN and COM2_TO_FPC_EN signals; it depends only on the state of the
ICMB_SOUT_EN signal.
Table 10-7: Allowed Combination of States
Main Power COM2_TO_FP_EN_L COM2_TO_SIO_EN Result
OFF Deasserted (1) Deasserted (0) COM2 disconnected
ICMB available†
ON Deasserted (1) Deasserted (0) COM2 disconnected
ICMB available†
OFF Asserted (0) Deasserted (0) COM2 routed to front panel
ICMB available†
ON Asserted (0) Deasserted (0) COM2 routed to front panel
ICMB available†
ON Deasserted (1) Asserted (1) COM2 connected with SMC*
ICMB available†
All Other States
Possible main power cycle
Possible component damage