Toshiba TMPR7901, Руководство пользователя

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Chapter 16: Clocks
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
16-1
16. Clocks
16.1 Overview
Clocks are one of the fundamental elements of the TX7901, which has three main clock
domains, which are depicted in Figure 16-1 and summarized in Table 16-1. By manipulating
the internal clock in different ways, the TX7901 can be controlled to run in different modes,
and at different clock speeds. Clock control is used for various I/O clock ratios and silicon
debug modes.
The TX7901 uses the following clocks as summarized below in Table 16-1.
Table 16-1 TX7901 Clocks
Clock Description
CPU Clock Basic clock supplied to the C790 core, data and instruction caches, and
MMUs
System Bus Clock
Supplied to the C790 bus and all the devices attached to it, SDRAMC,
G-bridge, and DMAC
G-bus Clock Supplied to all IPs (PCI, MAC, UARTS, SPI and Timer) connected to the
G-bus
The TX7901 clock system provides many different clocking options for all on-chip and
external devices. The Phase-Locked Loop circuitry can be used to provide a high-frequency
system clock from a low-frequency external source. Also, the TX7901 provides various
frequency dividers for a variety of clock domains on the chip. Figure 16-2 illustrates internal
clock source and distribution that includes the phased-locked loop, clock dividers, drivers,
and a generic IP.