Tut Systems SMS2000 - Manual (Page 85)

SMS2000 and Property Management Systems
TUT Systems, Inc Page 85 of 104 P/N 220-06288-20
That character is used to validate that the message was transmitted without errors. It is
calculated by adding up all of the characters in the message proceeding it (except the
STX and modulo the sum by 256).
The PMS has a limited time frame in which to respond with an ACK. The PMS may also
NAK the message for any reason. It is treated as a transmission error and the message is
sent again. After many tries, the SMS2000 gives up on this message and log it as an error
in the OCS.
Note: There is an optional second character.
ENQ-ACK-NAK MODE
ENQ-ACK-NAK mode provides reliable message delivery. It is similar to ACK-NAK
mode, but there is one additional interaction between the SMS2000 and PMS.
SMS ->
PMS ->
SMS -> This is the first message
PMS ->
SMS ->
PMS ->
SMS -> This is the second message
PMS ->
•
stands for the ASCII ENQ character, ASCII code 5 (Ox05).
Again the PMS must respond in a limited time frame to the ENQ as well as the message
to avoid retransmission. The PMS may NAK either the ENQ or the message.
Note:
There is an optional second character.