Conditions for response message, Delayed response – Beijer Electronics SCOM RBC EN User Manual
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Protocol Description and Timings
10
Beijer Electronics, MAEN993
Conditions for Response Message
The conditions for a response message generated by the Beijer Electronics RBC are
described below:
Delayed Response
If a Beijer Electronics RBC receives an SCOM message with a broadcast address from
the RS485 interface and the command is completed, the generated response message
is sent after a delay time. This is required, because many devices can be attached to
the RS485 bus, but only one device can claim the line for its communication. The
delay guarantees that each response message is sent one after one, even if all devices
have received the broadcast message and processed it at the same time, avoiding a col-
lision on the RS485 bus.
The length of the delay time depends on the device address and maximum length of
a response message, and is calculated according to the following formula:
Interface
Address condition
Command status
Response
RS232
Address does not match
device address
not EXECUTED
No response
not EXECUTED
No response
Address matches device
address
if COMPLETED
ACK
if FAILED
NAK
Address is Broadcast
address (0xFF)
if COMPLETED
ACK
if FAILED
NAK
RS485
Address does not match
device address
not EXECUTED
No response
not EXECUTED
No response
Address matches device
address
if COMPLETED
ACK
if FAILED
NAK
Address is Broadcast
address (0xFF)
if COMPLETED
Delayed ACK
if FAILED
No response
USB
Address does not match
device address
not EXECUTED
No response
not EXECUTED
No response
Address matches device
address
if COMPLETED
ACK
if FAILED
NAK
Address is Broadcast
address (0xFF)
if COMPLETED
ACK
if FAILED
NAK
(2.5 + Lr) x 10 x N
Te =
b
Te: Broadcast command response [s]
Lr: Maximum length of response message
N: Device address + 1
b: Baud rate [bits/second]