Clocking
As shown in Figure 42, the primary clock input (frequency) is multiplied up by the system phase-locked
loop (PLL) and the clock unit to create the coherent system bus clock (csb_clk), the internal clock for the
DDR controller (ddr_clk), and the internal clock for the local bus interface unit (lbiu_clk).
The csb_clk frequency is derived from a complex set of factors that can be simplified into the following
equation:
csb_clk = {PCI_SYNC_IN × (1 + CFG_CLKIN_DIV)} × SPMF
In PCI host mode, PCI_SYNC_IN × (1 + CFG_CLKIN_DIV) is the CLKIN frequency.
The csb_clk serves as the clock input to the e300 core. A second PLL inside the e300 core multiplies the
csb_clk frequency to create the internal clock for the e300 core (core_clk). The system and core PLL
multipliers are selected by the SPMF and COREPLL fields in the reset configuration word low (RCWL),
which is loaded at power-on reset or by one of the hard-coded reset options. See the chapter on reset,
clocking, and initialization in the MPC8349EA Reference Manual for more information on the clock
subsystem.
The internal ddr_clk frequency is determined by the following equation:
ddr_clk = csb_clk × (1 + RCWL[DDRCM])
ddr_clk is not the external memory bus frequency; ddr_clk passes through the DDR clock divider (÷2) to
create the differential DDR memory bus clock outputs (MCK and MCK). However, the data rate is the
same frequency as ddr_clk.
The internal lbiu_clk frequency is determined by the following equation:
lbiu_clk = csb_clk × (1 + RCWL[LBIUCM])
lbiu_clk is not the external local bus frequency; lbiu_clk passes through the LBIU clock divider to create
the external local bus clock outputs (LSYNC_OUT and LCLK[0:2]). The LBIU clock divider ratio is
controlled by LCCR[CLKDIV].
In addition, some of the internal units may have to be shut off or operate at lower frequency than the
csb_clk frequency. Those units have a default clock ratio that can be configured by a memory-mapped
register after the device exits reset. Table 57 specifies which units have a configurable clock frequency.
Table 57. Configurable Clock Units
Unit
Default Frequency
Options
TSEC1
csb_clk/3
csb_clk/3
csb_clk/3
csb_clk/3
csb_clk
Off, csb_clk, csb_clk/2, csb_clk/3
Off, csb_clk, csb_clk/2, csb_clk/3
Off, csb_clk, csb_clk/2, csb_clk/3
Off, csb_clk, csb_clk/2, csb_clk/3
Off, csb_clk
TSEC2, I2C1
Security core
USB DR, USB MPH
PCI and DMA complex
Table 58 provides the operating frequencies for the MPC8347EA TBGA under recommended operating
conditions (see Table 2). All frequency combinations shown in the table below may not be available.
Maximum operating frequencies depend on the part ordered, see Section 22.1, “Part Numbers Fully
MPC8347EA PowerQUICC II Pro Integrated Host Processor Hardware Specifications, Rev. 12
Freescale Semiconductor
77
FREESCALE [ Freescale ]
