Technical information

AT+i Commands Overview
1-4 AT+i Commands Reference Manual May 31, 2008
In auto baud mode, W24 expects an A or a character. This is usually the first character sent, since
in command mode a meaningful command is always prefixed by AT+i.
The host may send an a or A to the W24 to allow it to determine the host's baud rate. It may also
send a complete AT+i command. In any case, W24 detects the A or a character, determines the
correct baud rate, and configures its serial channel during the stop bit. Thus, the next character is
received by the serial port at the correct baud rate. The A itself is retained as well. W24 supports
auto baud rate detection for the following baud rates: 2400, 4800, 9600, 19200, 38400, 57600,
and 115200.
When the BDRF parameter contains a fixed baud rate, W24 initializes to the specified baud rate
without entering auto baud rate mode. Commands issued by the host must be sent using that baud
rate in order to be recognized. In this case, W24 can be forced into auto baud rate mode, refer to
“Entering Rescue Mode during Runtime” .
W24 dial-up mode only: When the BDRM parameter is set to an a value, W24 assumes the
attached modem has the auto baud rate feature. Once the host<>W24 baud rate is determined, the
W24<>modem baud rate is set to the same rate. Any other BDRM value is used as a fixed baud
rate to the modem.
High Speed USART
Very high baud rates, up to 3Mbps, can be reached between host and W24 via one of W24's
USARTs. The BDRD parameter acts as baud rate divider. When set to '0', W24 sets its host
USART baud rate according to the value of the BDRF parameter. When set to any value in the
range 1-255, it divides the maximum supported baud rate - 3Mbps - by that value. The quotient of
this division is set as the host baud rate, and the value of BDRF is ignored. For example, if BDRD
is set to 2, then the host baud rate will be 3Mbps-2=1.5Mbps.
If the W24<>modem interface is a USART, BDRD is set to any value other than '0', and the
modem baud rate is set to Auto (BDRM='a'), then the modem baud rate will be set to a fixed
value of 115,200bps.
In SerialNET mode, you can specify that host<>W24 baud rate over USART be determined by
the BDRD parameter. You do so by setting the first field of the SNSI parameter (<baud>) to '0'.
Entering Rescue Mode during Runtime
The MSEL (Mode Select) input signal of the W24 can be used for entering W24 into Rescue
mode.
If MSEL is pulled low (logical 0) for more than 5 seconds during runtime, W24 waits until MSEL
is pulled high (logical 1), performs a software reset and restarts in Rescue mode. In Rescue mode,
W24 performs the following operations:
• If in SerialNET mode - W24 exits SerialNET mode (changes SNMD value to 0).
• If serial baud rate (BDRF or BDRD) is set to a fixed value - W24 forces auto baud rate
detection. BDRF/BDRD value will be used again upon the next power-up.
• If Always Online mode is defined (TUP=2), or Automatic Router Start is enabled (ARS=1) -
W24 bypasses this mode, which means that W24 does not attempt to go online until the next
software or hardware reset.
• If the Host Interface parameter (HIF) is set to a fixed interface, it is forced into auto host
interface detection mode (HIF=0).