668-0011 Rabbit Semiconductor, 668-0011 Datasheet - Page 39

• Manufacturer Part Number: 668-0011
• Description: IC MPU RABIT3000A 55.5MHZ128LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0011

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 3000 8-Bit
• Speed: 55.5MHz
• Voltage: 2.5V, 2.7V, 3V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 128-LQFP
• Features: -
• Other names: 316-1043

4. S
M
YSTEM
ANAGEMENT
4.1 Overview
There are a number of basic system peripherals in the Rabbit 3000 processor, some of
which are covered in later chapters. The peripherals covered in this chapter are the periodic
interrupt, the real-time clock, the watchdog timers, and some of the miscellaneous output
pins and their control and processor registers that provide the processor ID and revision
numbers.
The periodic interrupt, when enabled, is generated every 16 clocks of the 32 kHz clock
(every 488 µs, or 2.048 kHz). This interrupt can be used to perform periodic tasks.
The real-time clock (RTC) consists of a 48-bit counter that is clocked by the 32 kHz clock.
It is powered by the VBAT pin, and so can be battery-backed. The value in the counter is
not affected by reset, and can only be set to zero by writing to the RTC control register.
The 48-bit width provides a 272-year span before rollover occurs.
There are two watchdog timers in the Rabbit 3000, both clocked by the 32 kHz clock. The
main watchdog timer can be set to time out from 250 ms to 2 seconds, and resets the pro-
cessor if not reloaded within that time. Its purpose is to restart the processor when it
detects that a program gets stuck or disabled.
The secondary watchdog timer, added in the Rabbit 3000A, can time out from 30.5 µs up
to 7.8 ms, and generates a Priority 3 secondary watchdog interrupt when it is not reset
within that time. The primary use for the secondary watchdog is to act as a safety net for
the periodic interrupt — if the secondary watchdog is reloaded in the periodic interrupt, it
will count down to zero if the periodic interrupt stops occurring. In addition, it can be used
as a periodic interrupt on its own.
The following other registers are also described in this chapter.
• Global Output Control Register (GOCR), which controls the behavior of the CLK,
STATUS, /WDT, and /BUFEN pins
• Global CPU Register (GCPU), which holds the identification number of the processor.
• Global Revision Register (GREV), which hold the revision number of the processor.
Chapter 4 System Management
29