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P4080 Development System User’s Guide, Rev. 0
24
Freescale Semiconductor
Architecture
Figure 15. Serial Architecture
The UART programming model is a standard PC16550-compatible register set. Baud rate calculations for
the divisor latch registers (DLL and DML) are typically done by reading the ngPIXIS PX_CLK register
to determine the P4080 SYSCLK clock input (typically 133 MHz) frequency, but possibly any value. The
baud rate divisors can then be calculated using the formula described in the P4080 QorIQ Integrated
Communications Processor Family Reference Manual.
NOTE: Programming Note
If the dynamic reconfiguration capabilities of ngPIXIS are used to set the
SYSCLK input to an arbitrary value, the 3 bits in the PX_CLK register are
not valid. In this case, the PX_AUX register is, by convention, set to the
value of SYSCLK in MHz, which is used in lieu of PX_CLK.
Note that the primary serial port is powered from the 3.3-V hot power rail, and thus may be used even when
the system is powered down. This facility is used by the ngPIXIS processor to run programs and interact
with the user, allowing reconfiguration of the board when sealed in the chassis.
5.1.14
I
2
C
The P4080 has four separate I
2
C/SMB buses; however, the P4080DS uses three of them. I
2
C1 is also
electrically isolated before power-up of the P4080 so as to allow ngPIXIS access to eeprom resources.
Those resources can be accessed by P4080 after power up. This figure shows the I
2
C block.
UART 1
LT
1331
Port #1
Port #0
P4080
UART 0
LT
1331
Top port
Bottom port
MUX
ngPIXIS
+3.3 V
HOT +3.3 V