Motorola 8900 User Manual - Page 41

Chapter 2: Hardware Interface Description Serial Interface During Low Power Mode During low power mode the C24 serial interfaces are disabled. This is indicated by the CTS signal high state. The C24 wakes up periodically from low power mode to page the network for any incoming calls or data. After this short paging is completed, C24 returns to low power mode. During this short awake period, the serial interfaces are enabled and communications with the module is possible. The CTS_N signal is alternately enabled and disabled synchronously with the network paging cycle. CTS_N is enabled whenever C24 awakes to page the network. This indicates the C24 serial interfaces are active (see Figure 2-7). Figure 2-7: CTS Signal During Sleep Mode The periodical enabling and disabling of the CTS_N signal during low power mode can be controlled by the AT+MSCTS command. Setting AT+MSCTS=1 permanently disables the serial interface during low power mode, even during a network page by C24. The CTS_N signal is disabled, and therefore the serial interfaces are blocked. Terminating Low Power Mode Terminating the low power mode, or wake-up, is defined as the transition of the C24 operating state from Sleep mode to Idle mode. There are several ways to wake-up C24 from low power mode as described below. Important: During power saving mode the C24 internal clocks and circuits are disabled, in order to minimize power consumption. When terminating the power saving mode, and switching to Idle mode, C24 requires a minimal delay time to reactivate and stabilize its internal circuits before it can respond to application data. This delay is typically of 15 milliseconds, and is also indicated by the CTS_N signal inactive (high) state. The delay guarantees that data on the serial interface is not lost or misinterpreted. December 15, 2008 C24 Module Hardware Description 17