STLC2500

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7.7.3

NO CONNECTION

If the Host places the UART in low power and there is no activity, then the STLC2500 can be placed in

Deep Sleep Mode. In this mode (no connection), the Host can also decide to put the STLC2500 in Com-

plete Power Down to further reduce the power consumption. In this case some part of the STLC2500 will

be completely powered off. It's possible to exit the Complete Power Down by using one of the two methods

explained in 7.8. The request to quit the Complete Power Down may be done with an HW reset or it may

come from the Host.

7.7.4

ACTIVE LINK

When there is an active link (SCO or ACL), the STLC2500 can go neither in Deep Sleep Mode nor in Com-

plete Power Down whatever the UART state is. But the STLC2500 baseband is made such that whenever

it is possible, depending on the scheduled activity (number of link, type of link, amount of data exchanged),

it goes in Sleep Mode.

7.8

SW initiated low power mode

During periods of no activity either on the Bluetooth or on the Host side, the chip can be placed in low

power mode. Two modes to initiate low power mode and to wake up are supported (selection is done

through pin configuration, see table 15):

1 [Initiated Low power, mode 1] It requires HOST_WAKEUP, UART_RXD (connected with

BT_WAKEUP, the two paths will be physically connected on the board) and UART_RTS. The

UART_RXD is used as wakeup signal from the host, the HOST_WAKEUP requires the clock from

the Host and the UART_RTS indicates when the controller is available. In this mode, the break func-

tion (UART_RXD is low for more than 1 word) is used to distinguish between normal operation and

low power mode usage.

The system goes in low power mode in this way: the Host tells the Bluetooth device that it can go in

low power by forcing the UART_RXD of the Bluetooth device to '0' for more than 1 word. Then, the

device can decide whether to go in low power mode or not depending on its scheduled activity. In

case it decides to go in low power mode, it signals it by forcing UART_RTS high; then it asserts

HOST_WAKEUP low to tell the Host that it does not need the clock anymore. The Bluetooth base-

band cannot go in sleep mode by itself. This is a logical consequence of the fact that the system clock

is needed to receive characters on the UART and only the Host can stop the UART link.

- The system wakes up in this way: the Bluetooth baseband first asks the Host to restart the system

clock by setting HOST_WAKEUP to '1'. When the clock is available, the device sets UART_RTS low,

and then the Host can give confirmation by releasing the UART_RXD of the device. In case the Host

wants to wake up the chip, it sets the UART_RXD pin of the Bluetooth device to '1'. The device then

confirms it is awake by releasing UART_RTS to '0'.

2 [Initiated Low power, mode 2] It requires HOST_WAKEUP, BT_WAKEUP, UART_RTS and

UART_CTS. The wakeup is always initiated by HOST_WAKEUP or BT_WAKEUP signal (the peer

acknowledges the request). UART_RTS and UART_CTS are placed at the value for which they block

the UART communication.

- The system goes in low power in this way: the Host sets BT_WAKEUP to '0', telling the Bluetooth

device that it can go in low power. The device can decide whether to go in low power mode or not

depending on its scheduled activity. If it decides to go in low power it first asserts UART_RTS pin to

'1' and then it sets HOST_WAKEUP to '0' to tell the Host that it does not need the system clock any-

more. The Host confirms by setting UART_CTS to '1' and by stopping the clock.

- The system wakes up in this way: the Bluetooth device sets HOST_WAKEUP to '1' to tell the Host

that it needs the clock. The Host delivers the clock, when the device is ready it releases UART_RTS

to '0'. Then the Host confirms by asserting BT_WAKEUP to '1' and by releasing UART_CTS to '1'. If

the Host wakes up first, it tells it to the Bluetooth device by setting BT_WAKEUP to '1'. The Bluetooth

device sets HOST_WAKEUP to '1' and then UART_RTS and UART_CTS are released by device and

Host respectively to tell they are ready to start communicating.