Timing Of The /Cts Signal In Cyclic Sleep Modes; Figure 9: Timing Of /Cts Signal (Example For A 2.12 S Paging Cycle) - Siemens MC45 Manual

MC45 Hardware Interface Description
P R E L I M I N A R Y
The CYCLIC SLEEP mode is a dynamic process which alternatingly enables and disables
the serial interface. The application must be configured to use hardware flow control. By
setting/resetting the /CTS signal, the module indicates to the application when the UART is
active. The application must wait until /CTS is set (i.e. is active low) on the physical UART
before data can be sent to the module.
The module starts or resumes power saving two seconds (AT+CFUN=5 or AT+CFUN=7) or
ten minutes (AT+CFUN=6 or AT+CFUN=8) after the last character was sent or received. It
resets the /CTS signal, and after additional 5ms, physically deactivates the UART to save
power. See Figure 10.
Note: If both serial interfaces RS-232(0) and RS-232(1) are connected, both are
synchronized. Although not explicitly stated, all explanations given in this chapter refer
equally to RS-232(0) and RS-232(1), and accordingly to /CTS0 and /CTS1.

3.3.2.4 Timing of the /CTS signal in CYCLIC SLEEP modes

The /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 and can be determined by 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.
If DRX > 3, i.e. if paging is performed at intervals from 0.71 to 2.12 seconds, each listening
period causes the /CTS signal to go active low. If DRX is 2, i.e. if paging is done every 0.47
seconds, the /CTS signal is activated with every 2
The /CTS signal stays active low for 20 ms. This is followed by another 5 ms UART activity.
Thus, once the /CTS signal goes active low, you have 25 ms to enter characters. In the
pauses between listening to paging messages, while /CTS is high, the module resumes
power saving and the AT interface is not accessible. See Figure 9.
Paging message
/CTS 20
ms
5 ms
AT interface disabled

Figure 9: Timing of /CTS signal (example for a 2.12 s paging cycle)

MC45_HD_01_V00.02a
Paging message
2.12 s
20
ms
5 ms
AT interface enabled
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nd
listening period.
Paging message
2.12 s
20
ms
5 ms
Paging message
2.12 s
20
ms
5 ms
12.08.2002