Conditions for response message, Delayed response – Beijer Electronics SCOM Protocol EN User Manual
Page 17

Protocol Description and Timings
Elektronik-Systeme Lauer, MAEN976
17
Conditions for Response Message
The conditions for a response message generated by the monitor are described below:
Delayed Response
If a monitor receives a SCOM message with a broadcast address from the RS485 in-
terface and the command is completed, the generated response message is sent after
a delay time. This is required, because many monitors can be attached to the RS485
bus, but only one monitor can claim the line for its communication. The delay guar-
antees that each response message is sent one after one, even if all monitors have re-
ceived the broadcast message and processed it at the same time, avoiding a collision
on the RS485 bus.
The length of the delay time depends on the monitor 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
monitor address
not EXECUTED
No response
not EXECUTED
No response
Address matches monitor
address
if COMPLETED
ACK
if FAILED
NAK
Address is Broadcast
address (0xFF)
if COMPLETED
ACK
if FAILED
NAK
RS485
Address does not match
monitor address
not EXECUTED
No response
not EXECUTED
No response
Address matches monitor
address
if COMPLETED
ACK
if FAILED
NAK
Address is Broadcast
address (0xFF)
if COMPLETED
Delayed ACK
if FAILED
No response
Ethernet
Address does not match
monitor address
not EXECUTED
No response
not EXECUTED
No response
Address matches monitor
address
if COMPLETED
ACK
if FAILED
NAK
Address is Broadcast
address (0xFF)
if COMPLETED
No response
if FAILED
No response
(2.5 + Lr) x 10 x N
Te =
b
Te: Broadcast command response [s]
Lr: Maximum length of response message
N: Monitor address + 1
b: Baud rate [bits/second]