
Agere Systems Inc.
29
Data Sheet
July 2001
T8302 Internet Protocol Telephone
Advanced RISC Machine (
ARM
)
4 Reset/Clock Management
The reset/clock management controller controls clock generation and clock selection; it maintains a real-time clock,
generates a power-on reset, and identifies the source of a reset condition. The block diagram of the reset/clock
management controller is shown below.
* Indicates the default position or setting.
5-9074(F)
Figure 3. Reset/Clock Management Controller Block Diagram
The reset/clock management controller contains the following features:
Clock Sources
I
EXT_CLK
input from an external 11.52 MHz crystal. This provides an input to generate the system
FAST_CLK
,
as well as an input that can be divided for the system slow clock. The crystal is connected to
XLO
and
XHI
.
I
RTC_OSC_CLK
input from an external 32.768 kHz crystal. This can provide an input to generate the
RTC_CLK
,
as well as the system
SLOW_CLK
.
The real-time clock circuit uses the 32 kHz
RTC_CLK
for maintaining elapsed real time and interrupting the
ARM
940T core at the programmed number of seconds if enabled. This real-time clock implementation does not
have a battery back-up feature so it is reset on all powerup resets. Pseudo real-time clock can be generated by
dividing
EXT_CLK
, using the
RTC external divider register
in systems without a 32 kHz crystal.
RTC_OSC_CLK
EXT_PROG_CLK
RTC EXTERNAL
DIVIDER
REGISTER
*
(0xB0)
SLOW
CLK
SWITCH
SLOW_CLK
ESCE
CMRT
SYSTEM
SWITCH
PLLC/CMEC
FAST CLK
SWITCH
EXT
PRESCALER
(0) RST
*
PLL
PRESCALER
(5) RST
*
USB
PRESCALER
(6) RST
*
PLL
VCO FREQUENCY
USB CLK
SWITCH
LOCK
PLL LOCK
DETECT
USB_CLK (48 MHz)
USBEXT/USBPLL
RF
FB
(FROM PLL)
57.6 MHz
SYS_CLK
EN_SDRCK
B_CLK
EXT_CLK
USB_ALT_CLK
POWER_UP
RESET
GENERATOR
V
SS
V
DD
EXT_RST
RESET SOURCE
REGISTER AND
CONTROLLER
WDG_RST
CLKOFF
RST0N
INT_RST
SDRCK
SOFT_RST
PWR_RST
XRTC0
XRTC1
32.768 kHz
*
PRESCALE_USB_CLK
PLL_CLK
PRESCALE_PLL_CLK
PRESCALE_EXT_CLK
FAST_CLK
KLC_CLK
EXTRTC
RTC_CLK
*
RTC
SWITCH
*
*
*