Westermo GD-01 - Manual (Page 190)

190 6196-2220
Description of the stages:
1. the DTE sends an AT command
2. the DTE drops DTR to make the DCE enter the power down mode.Warning:
this mode will not really enter until CTS is dropped (stage 4).The DTE could
also have dropped DTR after receiving the AT response (stage 3).
3. the DCE sends back the AT response (if any)
4. the DCE drops CTS and does enter the power down mode.
5. the DCE sends back an unsolicited response (for instance a RING or +SMTI
(incoming SMS indication))
6. the DTE wants to reply to that unsolicited response so it causes the DCE to
exit
the power down mode by raising its DTR.
7. in turn the DCE acknowledges the exit of the power down mode by raising
CTS.
8. & 9 exchange of AT commands/responses.
NOTE 1: The DTE must not send any AT commands from stage 2 on up to stage 7.
NOTE 2: During the latency period (between stages 2 and 4) should the DTE want to
abort the power down mode, it raises DTR and should wait for 150 µs
before assessing CTS. If CTS is still high than the DCE has aborted the power
down mode and is ready to receive AT commands.The 150 µs wait should
get around the race condition between DTR raise and CTS drop.
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