Telegesis (UK) Limited
TG-ETRXn-UG-01-103
26
User Guide
1.04
ETRX1 and ETRX2
©2008 Telegesis (UK) Ltd
ETRXn User Guide (Rev 1.04)
S31 represents the compare value of the 16-bit counter described above. Whenever reaching the
compare value I/O3 is cleared.
To produce a waveform of 800Hz and a 50% mark/space ratio on the ETRX2 we need to divide the
12MHz clock by 15000d = 0x3A98. This value is the top value of the counter at which I/O3 is set.
In order to achieve a 50% mark/space ratio the compare value needs to be half the top value,
namely 7500d = 0x1D4C. Those values are also the default values of S30 and S32.
The PWM output also serves as a DAC. If, as before, S2F=3A98 and S31=1D4C, then the mean
level is 0.5V
dd
. If S31 is halved to 0EA6 then the mean level is 0.25V
dd
though the frequency is
unchanged. The exact value and accuracy of V
dd
depends on the user‟s power supply.
S2F
S31
I/O3
Figure 15. PWM output and compare levels
Unlike the ETRX1, on the ETRX2 access to S2F and S31 is possible at any time, even when the
special function pin is disabled. This has no functional impact on the operation of I/O3, until the
special function pin is enabled by setting bit F of S2E.
7 Reviving An Unresponsive Module
If the module is completely unresponsive, it may be in power mode 3 or the serial port settings may
have been altered. Go to the “Download software” page of the Telegesis website and download
the
Factory Default Utility software
. Connect the mod
ule‟s serial port to your PC and run the
Factory Reset Tool; when prompted execute a hard reset by pulling the reset pin to ground or
pushing the reset button on a Development kit board. (The screening can is a convenient earthing
point.) If the serial port settings have been changed, resetting the contents of register S0B over
the air may solve the problem.
8 Security
Using the Telegesis AT command interface software 128-bit AES encryption is always enabled and
the settings of the main function register decide whether new nodes trying to join the network need
to have an identical encryption key (S03) or can obtain the key over the air from either a neighbour
or the coordinator. This means the decision whether to allow a node to join can be made either by
each routing node or by the coordinator only. In the latter case the coordinator acts as a so-called
trust centre
.
