Comtech EF Data DMD20 - Manual (Page 17)

DMD20/DMD50/DMD2050/DMD2050E/DMD1050/OM20 Remote Protocol Remote Operations
MN-DMDREMOTEOP Revision 9 1–7
DPARM_NOTIMPLEMENTED_ERROR 0x0622
DPARM_DATAINVERT_ERROR 0x0623
DPARM_SUMMARYFAULT_ERROR
0x0624
DPARM_EXTERNALEXCSOURCE_ERROR 0x0625
DPARM_ASYNCMODE_ERROR 0x062C
DPARM_ASYNCBAUDRATE_ERROR 0x062D
DPARM_ASYNCTYPE_ERROR 0x062E
DPARM_ASYNCDATABITS_ERROR 0x062F
DPARM_REACQ_SWEEP_ERROR 0x0631
DPARM_ESCCHANNEL1VOLUME_ERROR 0x0632
DPARM_ESCCHANNEL2VOLUME_ERROR 0x0633
DPARM_ESCOVERHEADTYPE_ERROR 0x0634
DPARM_TPCINTERLEAVER_ERROR 0x0635
DPARM_FASTACQENABLE_ERROR 0x0636
DPARM_RFMTIMECONSTANT_ERROR 0x0637
MDPARM_MAPNUMBER_ERROR
0x0A00
MDPARM_TIME_ERROR 0x0A01
MDPARM_DATE_ERROR 0x0A02
MDPARM_MINORALARMRELAYUSAGE_ERROR 0x0A03
1.2.5 Collision
Avoidance:
When properly implemented, the physical and logical devices and ID addressing scheme of the
COMMSPEC normally precludes message packet contention on the control bus. The importance
of designating unique IDs for each device during station configuration cannot be
overemphasized. One pitfall, which is often overlooked, concerns multi-drop override IDs. All too
often, multiple devices of the same type are assigned in a direct-linked ("single-thread")
configuration accessible to the M&C computer directly.
For example, if two DMD20 Modems with different addresses (DESTINATION IDs) are linked to
the same control bus at the same hierarchical level, both will attempt to respond to the M&C
computer when the computer generates a multi-drop override ID of 22. If their actual setup
parameters, status, or internal timing differs, they will both attempt to respond to the override
simultaneously with different information or asynchronously in their respective message packets
and response packets, causing a collision on the serial control bus.
To preclude control bus data contention, different IDs must always be assigned to the
equipment. If two or more devices are configured for direct-linked operation, then the M&C
computer and all other devices configured in the same manner must be programmed to inhibit
broadcast of the corresponding multi-drop override ID.
The multi-drop override ID is always accepted by devices of the same type on a common control
bus, independent of the actual DESTINATION ID. These override IDs with the exception of
“BROADCAST” are responded to by all directly linked devices of the same type causing
contention on the bus. The “BROADCAST” ID, on the other hand, is accepted by all equipment
but none of then returns a response packet to the remote M&C.
The following multi-drop override IDs are device-type specific, with the exception of
"BROADCAST". These are summarized below with ID values expressed in decimal notation:
Directly-Addressed Equipment Multi-Drop Override ID
Broadcast (all directly-linked devices) 00
DMD-3000/4000, 4500 or 5000 Mod Section, DMD20 01
DMD-3000/4000, 4500 or 5000 Demod Section, DMD20 02