Westermo GD-01 - Manual (Page 189)

189 6196-2220
Power down mode via RS-232
NOTE! Plese also refer to the AT+W32K command.
This appendix aims at describing how the power down mode of the product can be
activated and deactivated via the RS-232 serial link. In text below, the term “DTE”
refers to the customer device driving the product, which is referred to as the “DCE”.
The terms referring to the RS-232 signals and levels are used according to recommen-
dations V.24 and V.28. However they are worth at remembering:
DTR is the circuit 108/2,TX is the circuit 103, RX is the circuit 102 and CTS is the cir-
cuit 106.
The logical level “HIGH or ON” corresponds to positive electrical level according to
RS-232/V.24, whereas the level “LOW or OFF” corresponds to a negative electrical level
according to RS-232/V24
Basically the activation and deactivation is always initiated from the DTE and is carried
out through the handshaking of DTR and CTS.The power down mode can be entered
only when the DCE is idle, e.g.. when no connection to the network is in progress.
Whenever the DTE requests the DCE to enter the power down mode, the DTE drops
(ON-to-OFF transition) DTR. From this time on, the DTE must not send any more char-
acters on the TX line e.g.. even the TX FIFO must be empty.
The DCE acknowledges the power down mode by dropping CTS, which can occur at
maximum 5s after the DTR drop. However during that latency period the DTE is prohib-
ited from sending any more AT commands.
AT responses can be sent back to the DTE even if the DCE is in power down mode
(actually the DCE exits the power down mode, sends the AT response and enters back
the power down mode).Therefore the DTE can drop DTR just after sending an AT com-
mand and before receiving the AT response.
The DCE is made to exit the power down mode by raising the DTR. DCE is not ready
to receive further AT commands until it raises in turn CTS, which can take up to 2s from
the DTR raise.
Here below is a diagram depicting the handshaking:
B A C K