Technical information

Chapter 1: Introduction to AT+i Commands
May 31, 2008 AT+i Commands Reference Manual 1-3
Flexible Host and Modem Interfaces
The flexible host and modem interfaces feature enables users to select the interface through
which W24 accepts AT+i commands from the host processor, as well as the interface through
which AT+i commands are sent to a dialup or cellular modem.
Available host interfaces are:
• USART0
• USART1
• USART2
• USB Device (identifies itself as a CDC device)
• USB Host (supports only USB Modem class)
Available modem interfaces are:
• USART0
• USART1
• USART2
• USB Device
• USB Host
As a USB host/device, W24 supports the Full-Speed USB standard (12Mbps).
Host-to-W24 interface is selected by setting the value of the Host Interface (HIF) parameter. Any
value from 1 to 5 specifies a certain choice of interface, while a 0 value specifies automatic
interface detection. In automatic interface detection mode, the first character sent from the host
over one of the supported interfaces sets the host interface to be used throughout that session until
the next W24 power cycle.
When automatic host interface detection mode is enabled, a host is connected to one of the
USARTs, and the Host Fixed Baud Rate (BDRF) parameter is set to 'a' (automatic baud rate
detection), the first character the host has to send to W24 in order to trigger detection must be an
'a' or 'A'. If BDRF is set to a fixed baud rate, any character sent from the host triggers automatic
host interface detection.
In a similar fashion, a W24-to-modem interface can be selected using the Modem Interface (MIF)
parameter, except that automatic modem interface detection is not available.
Note that any changes to the HIF and MIF parameters take effect only after the following W24
power-up. Also note that W24 cannot be operated in SerialNET mode when the HIF parameter is
set to automatic mode. Sending an SNMD command (activate SerialNET mode) with HIF set to
automatic mode will result in an error message I/ERROR (122). In addition, any feature that
requires setting a fixed baud rate requires setting a fixed host interface, as well.
Hardware flow control is supported on USART0 and USART1 only. Hardware signal mirroring is
enabled only if the host and modem interfaces are set to either USART0 or USART1. See
description of Bit 2 of the FLW parameter.
Auto Baud Rate Detection
W24 supports auto baud rate detection on the host serial communications line. After power-up,
W24 enters auto baud mode when the BDRF parameter is set to the value 'a'. The AT+iBDRA
command forces W24 into auto baud mode while it is already in operation.