User's Manual

XT55/56 Hardware Interface Description
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XT55/56_hd_v02.06a Page 49 of 125 17.12.2004
The CYCLIC SLEEP modes give you greater flexibility regarding the wake-up procedures:
For example, in all CYCLIC SLEEP modes, you can enter AT+CFUN=1 to permanently wake
up the module. In modes CFUN=7 and 8, the GSM part of the XT55/56 automatically
resumes power saving, after you have sent or received a short message or made a call.
CFUN=5 and 6 do not offer this feature, and therefore, are only supported for compatibility
with earlier releases. Please refer to Table 11 for a summary of all modes.
The CYCLIC SLEEP mode is a dynamic process which alternatingly enables and disables
the serial interface. By setting/resetting the GSM_CTS signal, the module indicates to the
application whether or not the UART is active. The timing of GSM_CTS is described below.
Both the application and the module must be configured to use hardware flow control
(RTS/CTS handshake). The default setting of the GSM part of the XT55/56 is AT\Q0 (no flow
control) which must be altered to AT\Q3. See [1] for details.
Note: If both serial interfaces ASC0 and ASC1 are connected, both are synchronized. This
means that SLEEP mode takes effect on both, no matter on which interface the AT
command was issued. Although not explicitly stated, all explanations given in this
chapter refer equally to ASC0 and ASC1, and accordingly to GSM_CTS0 and
GSM_CTS1.
3.6.4 CYCLIC SLEEP mode AT+CFUN=9
Mode AT+CFUN=9 is similar to AT+CFUN=7 or 8, but provides two additional features:
• GSM_RTS0 and GSM_RTS1 are not intended for flow control (as in modes
AT+CFUN=5, 6, 7 or 8), but can be used to temporarily wake up the module. This way,
the module can quickly wake up and resume power saving, regardless of the GSM_CTS
timing controlled by the paging cycle.
• The time the module stays active after GSM_RTS was asserted or after the last character
was sent or received, can be configured individually using the command AT^SCFG.
Default setting is 2 seconds like in AT+CFUN=7. The entire range is from 0.5 seconds to
1 hour, selectable in tenths of seconds. For details see [1].
3.6.5 Timing of the GSM_CTS signal in CYCLIC SLEEP modes
The GSM_CTS signal is enabled in synchrony with the module’s paging cycle. It goes active
low each time when the module starts listening to a paging message block from the base
station. The timing of the paging cycle varies with the base station. The duration of a paging
interval can be calculated from the following formula:
4.615 ms (TDMA frame duration) * 51 (number of frames) * DRX value.
DRX (Discontinuous Reception) is a value from 2 to 9, resulting in paging intervals from 0.47
to 2.12 seconds. The DRX value of the base station is assigned by the network operator.
Each listening period causes the GSM_CTS signal to go active low: If DRX is 2, the
GSM_CTS signal is activated every 0.47 seconds, if DRX is 3, the GSM_CTS signal is
activated every 0.71 seconds and if DRX is 9, the GSM_CTS signal is activated every 2.1
seconds.
The GSM_CTS signal is active low for 4.6 ms. This is followed by another 4.6 ms UART
activity. If the start bit of a received character is detected within these 9.2 ms, GSM_CTS will