Question on the code, use of the registers

mayeranalytics / pySX127x

This is a python interface to the Semtech SX127x, HopeRF RFM9x, Microchip RN2483 long range, low power transceiver families.

GNU Affero General Public License v3.0

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Question on the code, use of the registers #29

Closed BMarvi closed 1 year ago

BMarvi commented 5 years ago

@mayeranalytics

return self.spi.xfer([register_address & 0x7F, 0])[1]
return self.spi.xfer([register_address | 0x80, val])[1]

can't understand the "& 0x7F" and "| 0x80" part.... why is necessary to modify the register address?

mayeranalytics commented 5 years ago

Have a look at section 4.3 of the datasheet:

The first byte is the address byte. It is comprises:

A wnr bit, which is 1 for write access and 0 for read access.
Then 7 bits of address, MSB first.

I.e. the intention to read or write is encoded in the highest bit of the address byte. The .. & 0x7F and .. | 0x80 set the highest bit to 0 or 1.