Datasheet

MPC8250 Hardware Specifications, Rev. 2
Freescale Semiconductor 19
Electrical and Thermal Characteristics
Figure 11 shows signal behavior in MEMC mode.
Figure 11. MEMC Mode Diagram
NOTE
Generally, all MPC8250 bus and system output signals are driven from the
rising edge of the input clock (CLKin). Memory controller signals,
however, trigger on four points within a CLKin cycle. Each cycle is divided
by four internal ticks: T1, T2, T3, and T4. T1 always occurs at the rising
edge, and T3 at the falling edge, of CLKin. However, the spacing of T2 and
T4 depends on the PLL clock ratio selected, as shown in Table 11.
Figure 12 is a graphical representation of Table 11.
Figure 12. Internal Tick Spacing for Memory Controller Signals
Table 11. Tick Spacing for Memory Controller Signals
PLL Clock Ratio
Tick Spacing (T1 Occurs at the Rising Edge of CLKin)
T2 T3 T4
1:2, 1:3, 1:4, 1:5, 1:6 1/4 CLKin 1/2 CLKin 3/4 CLKin
1:2.5 3/10 CLKin 1/2 CLKin 8/10 CLKin
1:3.5 4/14 CLKin 1/2 CLKin 11/14 CLKin
CLKin
V_CLK
Memory controller signals
sp34/sp30
CLKin
T1 T2 T3 T4
CLKin
T1 T2 T3 T4
for 1:2.5
for 1:3.5
CLKin
T1 T2 T3 T4
for 1:2, 1:3, 1:4, 1:5, 1:6