APPENDIX D: COMMUNICATION CODES
UNIFLOW
®
4 PULSED HEAT CONTROL
D-2 990-908
Section II. Control Communication Codes
RS-232 and RS-485 Communication Protocol
Each command will be formatted as follows:
<soh> <@> <cmd> <cnt> <data> <cksum> <eot>.
Definition of Command Elements
<soh> 1 BYTE The data packet will start with a SOH (start of header 0x01)
character .
<@> 2 BYTES This is the address of the unit to which data is requested converted
into ASCII decimal numbers. (“01" - “31"). Note: this is the RS-
485 unit address.
<cmd> 2 BYTES This is a two character ASCII string denoting the command.
(i.e. “SR”).
<cnt> 3 BYTES This is a count of data bytes to follow, converted into a ASCII
decimal number. (“000" - “999").
<data> n BYTES This is optional ASCII data formatted into fields with each field
separated by a comma
<cksum> 2 BYTES This is a two charter ASCII HEX string calculated from the sum
of all bytes except <soh>, <cksum>, and <eot> and then masked
with 255 (0xFF).
<eot> 1 BYTE This terminates the transmission. (End transmit 0x04).
Response to Errors or Unsupported Commands
The Control will respond to the receipt of incorrect transmitted data with a NAK command under the
following conditions.
The format of the NAK command string is:
<soh> <@> “NK” “001” <nak value> <cksum> <eot>.
Where <nak value> is: '1' NO <soh >. ‘2’ BAD checksum. ‘4’ Timeout.
‘3’ Unrecognized command. ‘6’ Data Bad.
There is No Acknowledgement sent when the data is correct and accepted by the Control.
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