072-0500
Alphasense User Manual
OPC-R1 Optical Particle Counter
Issue 1
Alphasense Ltd
Page 32 of 33
February 2019
Sensor Technology House, 300 Avenue West, Skyline 120, Great Notley. Essex.CM77 7AA. UK
Tel: +44 (0) 1376 556700 - Fax: +44 (0) 1376 335899
Email: [email protected] - Web: www.alphasense.com
In response to any initial command byte, the OPC-R1 should return a byte of value 0x31, indicating
it is busy.
Upon receiving a command byte OPC-R1 will stop its activities and prepare data for a response if
required.
During this period, until the response data is ready, if further bytes are sent to the OPC-R1, the
returned byte will continue to be 0x31 (busy). When the OPC-R1 has prepared its response data it
will load the SPI buffer with a byte value 0xF3 to indicate it is ready to transfer data.
The command byte value must remain consistent with the original command byte value sent for the
command to be validated by the OPC-R1. If it is not, the OPC-R1 will load the SPI buffer with 0x31
(busy) value and return to its normal mode of operation. THE SAMPLING TRIGGER WILL NOT BE
ARMED IF THIS OCCURS. Rearming of the trigger can be achieved by a successful histogram or
PM data request.
To communicate with the OPC-R1, the SPI master should poll the OPC-R1 with the command byte
value, checking the returned byte for the value 0x31 (busy) or 0xF3 (ready). The first returned byte
should always be 0x31 (busy). Subsequent returned bytes will either be 0x31 (busy) or 0xF3
(ready) depending on the status of the OPC-R1. If another byte value is received by the SPI master
at this stage, an error has occurred and communication should cease for > 2s to allow the OPC-R1
to realise the error and clear its buffered data. The SPI master should also clear any buffered data.
We recommend that the command byte polling interval is 10 ms and the delay between byte
transfers following a receipt of byte value 0xF3 (ready) is 10
m
s.