Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 59)

AN93
Rev. 1.3 59
Caution: Some U-register addresses are reserved for internal use and hidden from the user. Consequently, there
are gaps in the addresses of available U registers. Writing to reserved registers can cause unpredictable results.
Care must therefore be taken not to write to reserved or undefined register locations. This is especially likely when
writing to consecutive U-register addresses: all addresses covered by a conscutive write operation must be defined
and allowed to the user.
The AT command execution time is as long as 300 ms. The host must wait for a response after each command
(e.g., OK) before issuing additional commands. The reset recovery time (the time between a hardware reset or the
carriage return of an ATZ command and the time the next AT command can be executed) must also be respected,
as described in "2.1.1. Reset Sequence" on page 11.
Characters must not be sent between the ATDT command and the protocol message. During this time, the modem
is in a transition between command and data modes. Any characters sent during this time will cause the
connection attempt to fail.
Blind dialing (dialing without waiting for dial tone) is enabled by ATX0, ATX1, and ATX3. Whether or not blind
dialing is enabled, use of the W dial modifier causes the modem to look for a dial tone before dialing the number
string after the W. For example, an AT command string, ATX1 DT 9, W123456<CR>, causes the modem to dial 9
immediately without detecting a dial tone but does not dial 123456 until a dial tone is detected. AT commands and
result codes are listed in Tables 39–43. The default settings are shown in bold.
Table 38. Consecutive U-Register Writes on a Single Line
Command Result
AT:U00,0078,67EF,C4FA 0x0078 written to U00
0x67EF written to U01
0xC4FA written to U02
Table 39. Basic AT Command Set
Command Action
$
Display Basic AT command mode settings (see text for details).
Answer incoming call.
Re-execute last command (executes immediately, not preceded by
AT or followed by <CR>)
A
A/