This results in significant power reduction. Typically a DRX8 paging mode may
consume less than 2mA. This mode is often referred to as sleep mode.
In order to conserve the maximum amount of current, the UARTs (as well as other
normally active circuitry) also assume a low power state. The interface which controls
sleep in the GR/GS64 is the primary UART, through a handshake protocol between
two reciprocating signals.
The GR/GS64 sleep mode feature is enabled and disabled by using the AT command
AT*E2RS232. The factory default setting and the start-up default for this command is
for the UART not to support sleep mode handshaking. Sleep mode has to be enabled
by AT command each time the Wireless CPU® undergoes a power re-cycle.
Sleep mode can be negotiated when either the Host or the Wireless CPU® decides that
it no longer has any need to communicate with the other side. Either side can wake
up the UART interface when it has something communicate.
The two signals that drive entry into and exit out of this mode are DTR and DSR. DTR
is used by the Host to indicate that it wants to initiate sleep, or to acknowledge the
Wireless CPU®’s request to initiate sleep. Likewise, DSR is used by the Wireless CPU®
to indicate that it wants to initiate sleep, or an acknowledgement of the Host request
to initiate sleep.
If either UART requests entry in to sleep mode, the other UART must acknowledge the
request in a timely manner in order for sleep to be enacted. Sleep mode must not be
enacted until both UARTs have acknowledged the sleep mode request by the
appropriate DTR or DSR handshaking.
Before entering into sleep mode, the RTS and CTS signals should be set to indicate
that no data can be received by either UART, in order not to lose any data.
It is important to point out that even though this mode is called sleep mode, it is not
possible to accurately predict what the Wireless CPU® or Host will do in this mode,
since this is determined by network events and device configuration. The Host or
Wireless CPU® can enter a sustained sleep, where all activity is ceased, or it could
continue normal operation. The only requirement is that the UART interface lines
communicate the desire to sleep and that the DSR and DTR line can take the UART
interface back out of this mode.
The operating mode which specifically pertains to the ‘sleep’ mode described in this
document is also referred to as
Standby Handshaking in supplementary document
such as the GR64 & GS64 AT Command Manual.
2.4
Timing Diagrams
This section illustrates the interaction of the UART1 signal lines when entering and
exiting sleep mode.
APPLICATION NOTE
GR/GS64 UART Sleep Protocols
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