
46
MPC8245 Integrated Processor Hardware Specifications
MOTOROLA
System Design Information
1.7.3
Connection Recommendations
To ensure reliable operation, it is highly recommended to connect unused inputs to an appropriate signal
level. Unused active-low inputs should be tied to OVDD. Unused active-high inputs should be connected to
GND. All NC signals must remain unconnected.
Power and ground connections must be made to all external VDD, OVDD, GVDD, LVDD, and GND pins of
the MPC8245.
The PCI_SYNC_OUT signal is intended to be routed halfway out to the PCI devices and returned to the
PCI_SYNC_IN input of the MPC8245.
The SDRAM_SYNC_OUT signal is intended to be routed halfway out to the SDRAM devices and then
returned to the SDRAM_SYNC_IN input of the MPC8245. The trace length may be used to skew or adjust
the timing window as needed. See the Motorola application notes AN1849, the Tundra Tsi107 Design
Guide, and AN2164, MPC8245/MPC8241 Memory Clock Design Guidelines, for more information on this
topic. Note that there is an SDRAM_SYNC_IN to PCI_SYNC_IN time requirement (refer to
Table 10 for
the input AC timing specifications).
1.7.4
Pull-Up/Pull-Down Resistor Requirements
The data bus input receivers are normally turned off when no read operation is in progress; therefore, they
do not require pull-up resistors on the bus. The data bus signals are: MDH[0:31], MDL[0:31], and PAR[0:7].
If the 32-bit data bus mode is selected, the input receivers of the unused data and parity bits (MDL[0:31]
and PAR[4:7]) will be disabled, and their outputs will drive logic zeros when they would otherwise normally
be driven. For this mode, these pins do not require pull-up resistors and should be left unconnected by the
system to minimize possible output switching.
The TEST0 pin requires a pull-up resistor of 120
or less connected to OV
DD.
It is recommended that RTC have weak pull-up resistors (2–10 k
) connected to GV
DD.
It is recommended that the following signals be pulled up to OVDD with weak pull-up resistors (2–10 k):
SDA, SCL, SMI, SRESET/SDMA12, TBEN/SDMA13, CHKSTOP_IN/SDMA14, TRIG_IN/RCS2,
INTA, QACK/DA0 and DRDY. Note that QACK/DA0 should be left without a pull-up resistor only if an
external clock is used because this signal enables internal clock flipping logic when it is low on reset, which
is necessary when the PLL[0:4] signals select a half-clock frequency ratio and an external PLL is used to
drive the SDRAM device.
It is recommended that the following PCI control signals be pulled up to LVDD (the clamping voltage) with
weak pull-up resistors (2–10 k
): DEVSEL, FRAME, IRDY, LOCK, PERR, SERR, STOP, and TRDY. The
resistor values may need to be adjusted stronger to reduce induced noise on specific board designs.
The following pins have internal pull-up resistors enabled at all times: REQ[3:0], REQ4/DA4, TCK, TDI,
TMS, and TRST. See
Table 17 for more information.
The following pins have internal pull-up resistors enabled only while device is in the reset state:
GNT4/DA5, MDL0, FOE, RCS0, SDRAS, SDCAS, CKE, AS, MCP, MAA[0:2], and PMAA[0:2]. See
Table 17 for more information on the MPC8245 pins.
The following pins are reset configuration pins: GNT4/DA5, MDL[0], FOE, RCS0, CKE, AS, MCP,
QACK/DA0, MAA[0:2], PMAA[0:2], SDMA[1:0], MDH[16:31], and PLL_CFG[0:4]/DA[10:15]. These
pins are sampled during reset to configure the device. The PLL_CFG[0:4] signals are sampled a few clocks
after the negation of HRST_CPU and HRST_CTRL.