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Notes
79RC32438 User Reference Manual
3 - 1
November 4, 2002
Chapter 3
Clocking and Initialization
Introduction
This chapter discusses the reset initialization sequence that is required by the RC32438 device and
includes information on the boot vector settings. These settings are used to configure the processor for the
remainder of the power-up sequence. This chapter also provides a description of the clock signals that are
used on the RC32438.
Block Diagram
Figure 3.1 illustrates how the boot configuration vector and reset signals may be generated in a system.
Figure 3.1 System Block Diagram of Reset and Boot Configuration Vector Generation
Clocking Overview
The RC32438 is designed to simplify the external clocking requirements for an embedded system. The
device requires one input clock and from this generates the processor clock (PCLK) from which the CPU
pipeline operates, the clock for the DDR memory subsystem and the clock for the local address/data bus. If
the PCI interface is desired to be operated synchronously to the other RC32438 interfaces, the PCI clock
can be tied externally to the clock for the local address/data bus.
Internally, the device supports a range of clock multipliers and divisors to allow system designers to
select a combination that best meets their needs. Additionally, this device has been designed to operate
from a relatively low external clock frequency without compromising the CPU or memory performance. For
example, the use of a 33MHz clock can support a 266MHz CPU pipeline frequency and standard DDR 266
memories. In this case, the local memory bus can be operated at either 66MHz or 33MHz, enabling the PCI
interface to be operated from the same clock signal if synchronous operation is desired. The use of low
external clock frequencies simplifies board design and reduces noise emissions. Refer to Table 3.1 for more
information on the clock ratios that are supported.
High Speed
Device
or
Memory
F
BOEN
BDIRN
OE DIR
MDATA[31:0]
Low Speed
Device
or
Memory
FCT245
OE
.
.
Vcc
COLDRSTN
Reset
Generator
RSTN
External
Device
External
Device
External
Device
RC32438
(Boot vector)