Responses; Protocol Packet Definition; Packet Format - Honeywell SPM Technical Handbook

Responses

The SPM will accept a return communication for any
packet it sends. Your equipment may respond back with
an ACK, NAK, RESET packet or diagnostic dump.
The ACK packet is an acknowledgement to the SPM. It
indicates to the SPM that the last communication was
correctly received. The SPM will accept the ACK and no
further action will occur.
The other packet is the NAK. This type of packet is
translated as a NAK. It means that the last packet was
not received correctly. Either the check-character did not
match or there was some other communication error
(framing, for example).
The SPM re-sends the last packet if it receives an NAK
response. The SPM resends the message once. If the
resend fails, the SPM will not communicate (it will wait)
until the next regular communication activity occurs.
Table A-5 lists the valid response packets to the SPM.
Command
Command
Code (Hex)
ACK
20
(Acknowledgement)
NAK (Negative
21
Acknowledgement)
30 RESET
31 Diagnostic Dump
Table A-5: Valid Response Packets to the SPM
SPM Technical Handbook
Command Description
Indicates packet was received
properly.
Indicates the packet was not
valid. Will cause SPM to resend
the last packet of information.
Will cause SPM to do an Alarm
or Fault Reset, as if the RESET
button were momentarily
pressed.
The SPM will transmit the
software version and checksum
of the EPROM via command 35
(above).
SPM Single Point Monitor
A.2 Protocol Packet Definition
A.2.1 Packet Format
An SPM packet will follow the format described in Table
A-6 when transmitting.
Byte No.
Device Address. The address or "name" of the device this packet
1
is directed to. It is always (HEX) 4D.
Packet Length (n). The length is the number of bytes to be
2 found in this packet. It includes the address byte and the check-
character byte and all bytes between.
Command and Data. The remaining bytes within the packet
3 through (n-1)
are data bytes.
Check-character. This byte is the last character in the packet.
n Its value is equal to the negated summation of all previous bytes
in the packet. It is the negative checksum of the packet.
Table A-6: SPM Transmission Format
Graphically, the packet appears as shown in Table A-7.
Byte 1 Byte 2
Device Packet
Address Length
Table A-7: SPM Graphic Style
A-6
Function
Byte 3 through (n-1)
Commands and Data Set
Byte n
Check
Character