5.3.4.1 Set Central Initial Connection Parameter (ST,<hex16>…)

Format: ST,<hex16>,<hex16>,<hex16>,<hex16>

This command sets the initial connection parameters of the central device for future connections. This command expects four input parameters, and all are 16-bit values in hex format. For any modifications in current connection parameters, refer to 5.3.4.2 Request Connection Parameter Update (T,<hex16>…).

The corresponding get command, GT, returns the desirable connection parameters set by command ST when the connection is not established. When the connection is established, the actual connection parameters display in response to command GT.

Connection interval, latency and timeout are often associated with how frequently a peripheral device must communicate with the central device and are , therefore, closely related to power consumption. The following table provides details about the parameters, range and description.

The connection parameters need to adhere to the following rules.

Latency <= 30

Maximum Interval \times 1.25 \times (1 + L a t e n c y) \leq 4 \sec o n d s, (4 \sec o n d s = 400 m s)

Maximum Interval \times 1.25 m s \times (1 + L a t e n c y) \times 5 < T i m e - o u t \times 10 m s

Table 5-16. Connection Parameters
Parameter	Range	Description
Minimum interval	0x0006-0x0C80	The minimum time interval of communication between two connected devices Unit – 1.25 ms
Maximum interval	0x0006-0x0C80	The maximum time interval of communication between two connected devices Unit – 1.25 ms; must be larger or equal to minimum interval
Latency	0x0000-0x01F3 Must be less than ((Timeout10/Inter- val1.25)-1)	The maximum number of consecutive connection events. The peripheral device is not required to communicate with the central device.
Timeout	0x000A-0x0C80	The maximum time allowed between raw communications before the link is considered lost Unit – 10 ms


Default:	0010, 0010, 0000, 0048
Example:	`ST,0020,0064,0002,0064`	// Set the interval between 40-125 ms, latency to 2 events and timeout to 1s
Response:	`AOK`	// Success
Response:	`Err`	// Syntax error or invalid parameter
Note: The PDS stores these parameters. The parameters are effective immediately. Apple® iOS® devices have some special requirements for these parameters. The connection parameter update may be rejected if it does not comply with the rules. For more information, refer to the Accessory Design Guidelines on the Apple developer website.