28
EXCEPTION RESPONSES
When the master sends a query frame to an RVS-AXO, one of the following four
responses from the RVS-AXO is possible:
1. When no communication error is detected in the query, and no mistake is found by the
communication program module in the RVS-AXO, a normal response is returned.
2. If the RVS-AXO does not receive the query frame (for example because of
disconnected serial link cable) then no response is returned by the RVS-AXO. After
proper time the master will cause a timeout condition.
3. If the RVS-AXO receives the query, but a faulty CRC bytes and / or Parity bits are
detected, then no response is returned by the RVS-AXO. After proper time the master
will cause a timeout condition.
4. If no communication error is detected in the query, but the RVS-AXO communication
program module finds an error such as illegal Function, data address or data value, or
if the RVS-AXO is busy, then an Exception response is returned. The Exception
response includes Exception Code to inform the master about the type of the error.
Exception Code Response Frame:
Exception response frame holds fix number of 5 bytes. The first one, the Slave Address
field is the Serial link number (transmitted in query and identical to RVS-AXO Serial Link
No.). The second byte, the Function field returns the echo of the transmitted query
function, but with the Most Significant Bit set to 1 (adding $80 to the transmitted function
code). The third byte is the Exception Code informing about the type of error. Last two
bytes are the CRC bytes.
