PPC405GPR-3JB400Z datasheet(29/57 Pages) AMCC

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405GPr – Power PC 405GPr Embedded Processor

AMCC

Revision 2.04 – September 7, 2007

Data Sheet

Pull-Up and Pull-Down Resistors

Pull-up and pull-down resistors are used for strapping during reset and to retain unused or undriven inputs in an

appropriate state. The recommended pull-up value of 3k

Ω to +3.3V (10kΩ to +5V can be used on 5V tolerant I/Os)

and pull-down value of 1k

Ω to GND, applies only to individually terminated signals. To prevent possible damage to

the device, I/Os capable of becoming outputs must never be tied together and terminated through a common

resistor.

If your system-level test methodology permits, input-only signals can be connected together and terminated

through either a common resistor or directly to +3.3V or GND. When a resistor is used, its value must ensure that

the grouped I/Os reach a valid logic zero or logic one state when accounting for the total input current into the

PPC405GPr.

Unused I/Os

For some interfaces, it is possible to turn off input receivers for some or all of the signals by means of bit settings in

Refer to the PowerPC 405GPr Embedded Processor User’s Manual for details.

If receiver gating is not used, termination of some pins may be necessary when they are unused. Although the

PPC405GPr requires only the pull-up and pull-down terminations as specified in the “Signal Functional

Description” on page 30, good design practice is to terminate all unused inputs or to configure I/Os such that they

always drive. If unused, and receiver gating is not used, the peripheral, SDRAM, and PCI buses should be

configured and terminated as follows:

• Peripheral interface—PerAddr0:31, PerData0:31, and all of the control signals are driven by default. Terminate

PerReady high and PerError low.

• SDRAM—Program SDRAM0_CFG[EMDULR]=1 and SDRAM0_CFG[DCE]=1. This causes the PPC405GPr to

actively drive all of the SDRAM address, data, and control signals.

• PCI—The PCI pull-up requirements given in the Signal Functional Description apply only when the PCI

interface is being used. When the PCI bridge is unused, configure the PCI controller to park on the bus and

actively drive PCIAD31:0, PCIC3:0[BE3:0], and the remaining PCI control signals by doing the following:

- Strap the PPC405GPr to disable the internal PCI arbiter and to operate the PCI interface in synchronous

mode.

- Individually connect PCISErr, PCIPErr, PCITRDY, and PCIStop through 3k

Ω resistors to +3.3V.

- Terminate PCIReq1:5 to +3.3V.

- Terminate PCIReq0[Gnt] to GND.

External Bus Control Signals

All peripheral bus control signals (PerCS0:7, PerR/W, PerWBE0:3, PerOE, PerWE, PerBLast, HoldAck, ExtAck)

are set to the high-impedance state when ExtReset=0. In addition, as detailed in the PowerPC 405GPr Embedded

Processor User’s Manual, the peripheral bus controller can be programmed via EBC0_CFG to float some of these

control signals between transactions and/or when an external master owns the peripheral bus. As a result, a pull-

up resistor should be added to those control signals where an undriven state may affect any devices receiving that

particular signal.

The following table lists all of the I/O signals provided by the PPC405GPr. Please refer to “Signals Listed

Alphabetically” on page 16 for the pin number to which each signal is assigned.

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