Product Info

Bluetooth Serial Module

AT Command Set

Date : 3 Feb 03 Issue No : 1.9 Doc No : XRBLU020-001SW-0 Page 26 of 38

10. Power Consumption and Reset

10.1 Reset

The module can be reset by the host without the need of any i/o using a BREAK signal. The module has

been configured to reset when the RX line detects a break condition for durations greater than 100

milliseconds.

10.2 Power Consumption

The current drain from the Vcc power input line is dependent on various factors. The three most significant

factors are the voltage level at Vcc, UART Baudrate and the operating mode.

The hardware specification for the serial module allows for a voltage range of 3.6 to 6.0v at Vcc. Tests

have shown that there is no significant difference in current draw when Vcc is 5 or 6V. Therefore the data

presented below, pertains to Vcc levels of 3.6 and 5v only. Tests have shown that where power drain is an

issue, it is best to keep Vcc at the lower end of the range.

The UART baudrate has a bearing on power drain because as is normal for digital electronics, the power

requirements increase linearly with increasing clocking frequencies. Hence higher baudrates result in a

higher current drain.

Finally with regards to operating mode the significant modes are; idle, waiting for a connection, inquiring,

initiating a connection and connected. With connected mode, it is also relevant to differentiate between do

data being transferred and when data is being transferred at the maximum rate possible.

The operating mode can best be described by stating the AT commands required to enter that mode. In

addition, there are certain S Registers which have a direct impact on power consumption, which are

described next.

The serial module has 2 Leds which can be configured to display connection status. One led is used to

display connection status, while the other is used to either display ‘Ring Indicate’ status or follow the state

of the incoming DSR line on the UART interface. Tests have shown that these Leds can consume up to

5.3mA which is more than double the current draw when in Idle mode. Therefore S registers 533 and 534

can be used to completely disable these indications.

Finally S Registers 508 to 511, which specify the page and inquiry scan intervals and windows, can be

used to adjust the average current drain when in discoverable and or connectable modes. Registers 508

and 509 specify the interval and window for page scans and registers 510 and 511 specify the interval and

window for inquiry scans. Register pairs 508/509 and 510/511 describe duty cycles when the serial

module goes into scan modes. It is while scanning that the highest current draw occurs. The average

current draw is determined by simple arithmetic using the values stored in the 508/509 and 510/511

The operating modes described above are entered using AT commands as follows:-

Idle On power up, with S Reg 512 = 1

Wait for Connection AT+BTG (100% page scan duty cycle)

Discoverable Only AT+BTQ (100% inquiry scan duty cycle)

Connecting ATD

Connected No Data