Specifications
ISU AT Command Reference  S-Register Definitions 
Iridium Proprietary Version 2.45 
20 June 2011     111 
12 S-Register Definitions   
S-registers allow control over specific ISU modem operations. Some S-registers contain a single numeric 
value. Other S-registers are bit mapped where individual bits, or sets of bits, control specific functions. 
12.1 S-Register Commands 
Commands allow S-registers to be read, written,, or simply referenced (i.e. set a pointer to designate the 
current, referenced S-register). S-register commands are described in the following subsections. 
12.1.1  Sr - Direct S-Register Reference 
Set a pointer to reference S-register r. 
12.1.2  Sr? - Direct S-Register Read 
Read the value of S-register r. 
12.1.3  Sr=n - Direct S-Register Write 
Set the value of S-register r to n, where n is a decimal value in the range 0 to 255. 
12.1.4  ? - Referenced S-Register Read 
Read the value of the current referenced S-register. The current referenced S-register is that which was last 
acted upon by a direct reference (ATSr), read (ATSr?), or write (ATSr=n) command. 
12.1.5  =n - Referenced S-Register Write 
Set the value of the current referenced S-register to n. The current referenced S-register is that which was 
last acted upon by a direct reference (ATSr), read (ATSr?), or write (ATSr=n) command. 










