Siemens SIMATIC ET 200SP HA Manual page 73

Structure of the HART-specific settings
Figure B-1
* When the number of HART preamble bytes = 0, the number of preamble bytes required by
the connected field device are used, but no fewer than 5.
When the number of HART preamble bytes = 255, then 20 preamble bytes are used.
Analog Input Module AI 16xI 2-wire HART HA ( 6DL1134-6TH00-0PH1)
Manual, 11/2017, A5E39408968-AB
Settings
HART operating data records
B.6 HART-specific settings
73