4 Honeywell Sensing and Control
Honeywell Zephyr
TM
Digital Aiflow Sensors
HAF Series–High Accuracy, 10 SLPM, 15 SLPM,
20 SLPM, 50 SLPM, 100 SLPM, 200 SLPM or 300 SLPM
Rev. B
50080060
Table 10. Sensor Response Descriptions
Sensor Response
(Hexadecimal)
Response Name Response Description
0xCCA5 POSACK non-response command was executed successfully
0xCC99 BadCommand command byte was not recognized
0xCC9A BadParam command sent with incorrect parameter bytes
0xCC9B Failure command failed during execution
0xCC90 BadChecksum checksum did not match stored value
0xCCBB Busy sensor is busy calculating the checksum value
Table 9. User Command Descriptions
Command Byte
(Hexadecimal)
Command Name Command Description
Command Response Time
(Max.)
0x01 GetSerialNumber
Next two read requests will each return two bytes of the
sensor’s unique 4-byte Serial Number.
10 ms
0x02 PowerOnReset Force Power-On reset of sensor microcontroller. 20 ms
0x03 Checksum
Calculates EEPROM Checksum and compares to pro-
duction Checksum value. If the values match, the next
read request will respond with 0xCCA5. Otherwise, the
next read will respond with 0xCC90.
1 s
10
Figure 2. Sensor I
2
C Read and Write Sequences
Start condition
S A6 A5 A4 A3 A0A2 A1 1 SA D7 D6 D5 D3 D2 D1 D0 MA D6 D4 D3 D2 D1 D0 MN SD4 D5D7
A
SCL
S A6 A5 A4 A3 A0A2 A1 1 SA D7 D6 D5 D3 D2 D1 D0 SA SD4
A
SCL
Stop condition
Address bit
Read/write bit
Data bit
Slave ACK
Master ACK
Master NACK
S
S
D7
A6
1
SA
MA
MN
Master pulls SDA from high to low while SCL remains high
Master allows SDA to float from low to high while SCL remains high
I
2
C Slave Address is the 7 Most Significant Bits for the first transmitted byte
Read = 1, Write = 0
Slave pulls SDA low
Master pulls SDA low
Master allows SDA to float high
I
2
C Read: Slave responds to Master with data
Data Byte 0 (Most Significant)
Data Byte 1 (Least Significant)
Command Byte
I
2
C Read: Master sends data to Slave
Bit Name Description
The maximum sink current on SCL or SDA is 2 mA. Therefore, if the pull-up resistors are biased by VDD, and if VDD reaches the maximum
supply voltage of 6 V, then the pull-up resistors for SCL and SDA must be greater than 3.0 kΩ to limit the sink current to 2 mA. The typical
value for SCL and SDA pull-up resistors is 4.7 kΩ (this value depends on the bus capacitance and the bus speed).
After the power-up read sequence described above, the sensor will respond to each I
2
C read request with a 16-bit (2 byte) digital flow
reading. Read requests taken faster than the Response Time (1 ms) are not guaranteed to return fresh data. The first two bits of each
flow reading will be ‘00’, while non-flow responses (such as error and status codes) will begin with ‘11’. There are several user com-
mands available as shown in Table 9. Following an I
2
C write sequence of a user command, the sensor will respond to the next I
2
C read
request with a 16-bit response. Possible responses to user commands can be seen in Table 10.
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