SH3000 SEMTECH [Semtech Corporation], SH3000 Datasheet - Page 7

• Manufacturer Part Number: SH3000
• Description: Low-Power Programmable Multifunction Support IC for Microcontrollers
• Manufacturer: SEMTECH [Semtech Corporation]

periodic reload of the time-out value, triggered by a write
of a code byte to the Watchdog Reload Register. As a
further safety measure, there are two different and
alternating code bytes that should be written to the same
Watchdog Reload Register. The code values are 0x5A
and 0xC3. The timer is reloaded after every write of a
single code byte.
Reload Register, or reset is activated when the
watchdog timer expires. Also, reset is initiated
immediately if the value of the code byte is incorrect or
out of sequence. When the watchdog triggers the reset,
its duration is 12 ms.
one of the code values, results in the highest level of
system security. These routines must execute in the
correct order. It is unlikely that runaway code could
manage this. In addition, this design makes it difficult for
the code to become stuck in a tight loop resetting the
watchdog.
Clock Management System
managing clocks, a versatile and accurate “any
frequency” clock synthesizer (see Figure 4).
range of 62.5 kHz to 16.0 MHz, with worst-case
resolution of 0.0256% (256 ppm). The internal 32 kHz
clock can also be routed to the CLK
oscillator stopped for energy savings).
Management System are aimed towards the systems
that utilize a microcontroller, a microprocessor, a DSP or
an ASIC.
Copyright ©2003-2005 Semtech Corporation
SYSTEM MANAGEMENT
32.768 kHz
The watchdog timer is kept from timing out by
The code byte should be written to the Watchdog
Using two separate software routines, each to write
The SH3000 provides a flexible tool for creating and
It is capable of generating any frequency in the
The objectives, features, and behavior of the Clock
÷
16
From / To
Serial I/O
2048 Hz
Frequency Locked Loop
Frequency
Set value
13-bit
Logic
OUT
Figure 4. Simplified HF Oscillator System
pin (and HF
FLL On
7
Random Noise
8-bit Pseudo
Generator
intentions of the host processor, an industry first. The
SH3000 shuts down its clock output when it senses that
the host processor issued a STOP instruction.
Subsequently, the SH3000 idles, consuming less than
10 µA. As soon as the host exits the STOP mode, the
SH3000 instantaneously starts to supply a stable clock
(<2µs wake-up).
resonator or a crystal as the frequency determining
element, must wait at least several hundred
microseconds (for a resonator), or as much as 100 ms or
more (for a HF crystal), to re-start the oscillator. The
SH3000 allows the response to and service of an event
to finish with a speed previously unattainable for a
simple microprocessor. A system with a traditional clock
approach may be as much as 100x – 10,000x slower.
Clock Generator Operation
constructed from the 2:1 tunable 8.0 –16.0 MHz HF
oscillator followed by a programmable “power-of-two”
post-divider (see Figure 4).
post-scale divider allow instantaneous switching
between the 32 kHz internal clock and divided-down HF
oscillator output. There is no settling or instability when
the switch occurs.
computing systems, when the large ratio between high
and low frequency of operations allows for
correspondingly large and instantaneous savings in
power consumption.
8, 16, 32, 64, 128)
The SH3000 permits the automatic sensing of the
A typical system, constructed with a ceramic
The frequency synthesizer in the SH3000 is
The Clock Source selector and the programmable
This is a preferred method for clock control in
(Divide by 1, 2, 4,
DCO Code
Register
18-bit
Post-scaler
Spreading
Clock Source
Spectrum
Controls
SH3000 MicroBuddy™
1
0
V1.15
Clock Buffer
HF Digitally
Controlled
8-16 MHz
Oscillator
and Glue
Logic
www.semtech.com
Clock On
S
TART
/S
CLK
CLK
16
15
DCO On
TOP
Force
OUT
IN