
155
42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
32Bit Symbol Counter
compare
unit 1
interrupt
generation
320s
backoff slot
counter
configuration
register
compare
unit 2
compare
unit 3
clock
prescaler
clock
select
SFD
timestamp
Beacon
timestamp
3
2
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z
R
T
C
1
6
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z
x
ta
l
A
V
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10 MAC Symbol Counter
Figure 10-1. Symbol Counter Overview
10.1 Main Features
The MAC symbol counter provides symbol timing information for IEEE 802.15.4
wireless networks. The counter time base can be derived from the 16 MHz crystal or
the RTC (32.768 kHz crystal on TOSC) during operation. In deep-sleep mode the
counter operates from the RTC clock. The module provides the following features:
Backoff slot counter with interrupt generation
Counter clock source selection between XTAL1 (16 MHz) and TOSC1 (RTC)
Automatic RTC clock selection for sleep mode operation and automatic
fallback
3 independent compare units with relative and absolute compare mode and
interrupt generation (support for slotted operation and superframe handling)
Low-power, deep-sleep mode operation and system wake up with all symbol
counter interrupt events
Automatic SFD and incoming beacon timestamping
Manual beacon timestamping
Manual timer synchronization within a 16 s symbol period by resetting clock
prescaler and backoff slot counter
Atomic read/write access for 32 bit registers
10.2 Clock source selection and Sleep/Active mode operation
The symbol counter can be sourced by the transceiver clock or by the asynchronous
Real Time Clock (RTC) oscillator. If the transceiver goes from active mode into sleep
mode, the symbol counter clock source is switched to the RTC clock automatically. A