Comtech EF Data CRS-200 REDUNDANCY SWITCH - Manual (Page 48)

CRS-200 COMTECH COMMUNICATIONS CORPORATION
CRS-200 REDUNDANCY SWITCH - OPERATIONS MANUAL PAGE 46
In RS485 applications, the same indexing of the modems based on the switch’s address still
applies. Now, however, the switch itself may be set to 1000, 3000, 5000 or 7000. This
allows up to 4 switches to be connected on the same bus. For example, if the base address
of the switch is set to 5000, the address of TM #3 is 5300. Note that in either RS232 or RS485
mode the internal link from the switch to all the modems connected to it
is fixed at RS232.
This means that the modem addresses (0100-1100) do not have to be set on each modem.
Since they are in RS232 mode,
their addresses stay at 0000. Commands are routed by the
switch to the appropriate modem based on the position of its TM Interface.
Important note: The controller sends a packet with the address of a target - the destination
of the packet. When the target responds, the address used is the same address, to indicate to
the controller the source of the packet. The controller does not have its own address.
INSTRUCTION CODE
This is a three-character alphabetic sequence that identifies the subject of the message.
Wherever possible, the instruction codes have been chosen to have some significance. For
example, TFQ is for transmit frequency, BKH is for backup holdoff, etc. This aids in the
readability of the message if seen in its raw ASCII form. Only upper case alphabetic
characters may be used (A-Z, ASCII codes 65 - 90).
INSTRUCTION CODE QUALIFIER
This is a single character that further qualifies the preceding instruction code.
Code Qualifiers obey the following rules:
1) From Controller to Target, the only permitted values are:
= (ASCII code 61)
? (ASCII code 63)
They have these meanings:
The ‘=’ code (controller to target) is used as the assignment operator, and is used
to indicate that the parameter defined by the preceding byte should be set to the
value of the argument(s) that follow it. For example, in a message from controller
to target, TFQ=070.0000 would mean ‘set the transmit frequency to 70 MHz’
The ‘?’ code (controller to target) is used as the query operator, and is used to
indicate that the target should return the current value of the parameter defined by
the preceding byte. For example, in a message from controller to target, TFQ?
would mean ‘return the current value of the transmit frequency’