Comtech EF Data SDM-300A - Manual (Page 284)

SDM-300A Satellite Modem Revision 6
ASYNC/AUPC Interface MN/SDM300A.IOM
11–2
ASYNC overhead is a 1/15 rate overhead channel composed of the following:
• Framing information
• EIA-232 or EIA-485 data
• Valid data flags
• AUPC information (if installed)
• Parity bits
The rate of asynchronous data transfers may be selected by the operator, with the
maximum rate available limited to 1.875
% of the synchronous data rate.
Note: The asynchronous overhead structure is an Comtech EF Data standard, and is not
compatible with IBS or IDR overhead formats.
The ASYNC interface PCB also provides its own Doppler buffer, which has a maximum
depth of 32 ms at the highest terrestrial data rate. Buffer fill status can be checked in the
Monitor menu on the front panel of the modem. Depth selection and centering of the
buffer are provided in the Configuration Interface menu.