file: sht75if_cmd.html
7 Dec 2012
SHT75IF SENSIRION RH & AT PROBE BOARD VERSION 2.xx COMMAND SET
The SHT75IF probe, using the Sensirion SHT75 sensor, is intended to replace the Rotronics MP-101A probe and VOSHPS interface board combination used in ASIMET modules up to the present (early 2013). For compatibility, the SHT75IF address is HPS01 and the 'M', 'N' and 'P' command responses are unchanged. The only modification required is to move the Sensor Comms Select jumper (JP1) on the main VOSC530 CPU board to the RS232 position (jumper pins 1 & 2) to match the SHT75IF probe RS232-only comms.
Refer to Latest Version Information for
reference info on latest firmware version numbers.
Note: commands sent are indicated in BOLD, responses in normal text.
<crlf> represents ASCII carriage return and line feed.
Command Description
- A Address acknowledge
- returns address of module, terminated by <crlfetx>
- example:
#HPS01A HPS01<crlfetx>
- NOTE 1: HPS01 is the default address of the SHT75IF probe as well
as the original HPS module;
it may be changed by the 'UOK' command but any failure of
EEPROM will result in the use of the default address. In
addition, use of defaults is reported in the 'L' command.
- C Output calibrated data
- Output calibrated interval mode data; also switch
to 1 minute interval mode if currently in polled mode
- outputs most recent calibrated values of relative humidity
in %, air temperature in degrees C.
That is, as follows:
rh% degC <crlf>
- example:
#HPS01C 65.325 24.337<crlf>
- C language format: "%7.3f %7.3f\r\n\x03"
- NOTE: sensor power is turned ON before each 1 minute reading per the O
setting under UOK command.
- H Help
- #HPS01H - a multiple line response with text similar
to the first line of each command description in this
document as the help line, with each line terminated
<crlf> and final line terminated <crlfetx>, as follows:
Firmware SHT75IF v2.00
A - Address acknowledge
C - Calibrated data (and goto interval mode 1)
H - Display Help message
L - Report ID, serial #, cal info
M - Report cal constant set 1: A B C D
N - Report cal constant set 2: A B C D
P - Calibrated data (and goto polled mode 0)
T - Enter test mode
U - Update EEPROM constants - password 'OK'
- A,Cxy,D,M,N,Q,S,WOK
- L Report ID, serial #, cal info, etc.
- M Output first set of calibration constants
- returns cal set #1 (RH) values A B C D without heading, space
separated (for easy access from ASIPIC24 Main CPU board)
- example:
#HPS01M -2.04680e+00 3.67000e-02 -1.59550e-06 0.00000e+00
- N Output second set of calibration constants
- returns cal set #2 (TEMP) values A B C D without heading, space
separated (for easy access from ASIPIC24 Main CPU board)
- example:
#HPS01N -3.97000e+01 1.00000e-02 0.00000e+00 0.00000e+00
- P Output polled mode data; also switch
to polled mode if currently in 1 minute IMET-style interval mode
- outputs same info as 'T' command, i.e. both calibrated and
raw data, after slight delay to acquire new data.
- sensor power is always ON in this mode.
- T Enter test mode
- UOK Update EEPROM contents
- enters the update mode after confirmation of 'OK' password.
New EEPROM values may be entered in this mode.
- upon initial entry, you must send the letters OK after the
command or the command is ignored, e.g. #HPS01UOK may be sent
as one. Upon receipt of the correct 'password', the response will
be OK if current parameters are valid, or NEW if parameters
have never been entered or are suspicious (i.e. EEPROM failure or
bad internal checksum).
- response to an unknown command is '?'
- IMPORTANT! command letter or letters A, Cxy, O, or S
will respond with the current setting when issued followed
by <cr> only . If followed by =xxxxx<cr>, where xxxxx is some
appropriate value, the EEPROM setting will be changed pending
receipt of 'WOK' command to make it permanent. Subsequent
requests for current settings will report the new value while
still in update mode. However, if update mode is exited with
'Q', the original settings of all parameters will remain intact.
- the following commands are available in EEPROM update mode:
- A - module Address (1 to 5 characters)
- Cxy - Cal Constants, where x is set 1 or 2, and y is
constant A to D
- O - Sensor ON time (1 - 30 seconds, default 5) before taking a reading
(only for IMET-style interval mode)
- Q - Quit without writing new info to EEPROM
- S - Serial number
- WOK - Write new info to EEPROM and exit
- Cal Constant Sets apply as follows:
- Cal constants are used in a polynomial of form:
A + Bx + Cx^2 + Dx^3
- examples:
- To see the current module address:
A<cr>
- To change the current module address:
A=HRG01<cr>
- To see the current C2A cal constant (set 2, constant A):
C2A<cr>
- To change the current C2A cal constant:
C2A=-39.7<cr>
- NOTE: Upon completion, the newly updated module address
will not take effect until the next reset or power-up.
Revision history:
- Original Release - 2 Nov 2012
- Rev A - 7 Dec 2012