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The second byte returned with all command headers is the results of the last SPI communication.
These codes indicated any errors associated with the communication, and are detailed in Figure
21.
SPI Error Codes
No Errors
Last communication was under clocked
(not all data was received)
Last communication was over clocked
(Excess data was sent and ignored)
Busyness
Each byte received by the sensor must be processed after reception. If the clock rate is relatively
low, processing can be done during the clock cycle. However, it may be necessary to include a
time allowance between bytes for processing as indicated below.
Item
Time
T1
>1us
T2
>0.5 µs*
T3
>1 µs*
Processing begins when the SS ( ������������) line is raised after a command is received from the
master (user controller). During processing, the sensor has limited capability to respond. For
example, after issuing a MEAS? or READ?, the process of collecting the averaged measurement
begins. During this time the sensor will report as busy in one of the two ways detailed below.
Busy/Ready
The Busy/Ready byte is always the first byte returned with the Command Header. While waiting
for a measurement to complete, checking using Command Header 06H is recommended. It will
return the Busy/Ready byte, the communication error byte, the Sensor Status byte and the
length of any available data. If the Busy/Ready byte is not zero, the sensor cannot process further
instructions. When using Header 06h, the entire 6 bytes must be read in each time or an SPI error
will be indicated on the next communication. When Busy/Ready is zero, the sensor can accept
commands. This does not indicate that a measurement is complete and will occur while the
sensor is processing measurements. Commands such as *DCL can be sent at this time to clear the
DOC: SPII2CHDWBrief - V2.71 07/25/2017
Figure 21 – SPI Error Codes
T3 Note: After T3 has elapsed, a processing time allowance
*
must be included so that the sensor has time to process the
request. Several milliseconds may be required for non-
measurement commands. T2 Note: If clocking rate is below
1MHz, the T2 ½ cycle does not need to be stretched.
Figure 22 - Byte Timing Diagram and
Header
E0h
E1h
E2h
Table●
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