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-- functions to write registers over microwire interface
-- it resembles SPI but need exrta pin which sends Load Enable (LE) pulse
-- otherwise SPI sequence is sent into 24 bit FIFO buffer
-- Pins assignment
-- SPI Id selects which pins are used for CLK, MOSI, MISO, CS
spiID = 1; -- ID=1 --> HSPI in nodemcu language
databits=24; -- LMX2487 loads 24 bits sequence per write into a register
-- default SPI clock is 80 MHz
fSPI = 80000000
-- lmx2487 can handle up to 20 MHz speed (50 nS per clock) but optocoupler is good for 240kHz
-- so let's aim for 100 kHz
maxMicrowireInterfaceSpeed = 100000; -- in Hz
clock_divider = math.floor(fSPI/maxMicrowireInterfaceSpeed)
-- we will use SPI ChipSelect pin for LoadEnable pin
microwire_LE_pin = 8; -- microwire Load Enable pin. 8 --> GPIO15
function microwire_setup_interface ()
-- now microwire <--> SPI setup
-- microwire is SPI with CPOL=0 and CPHA=0 i.e. SPI mode 0 = 00 = CPOL.CPHA
-- see https://en.wikipedia.org/wiki/Serial_Peripheral_Interface#Mode_numbers
-- see https://www.totalphase.com/support/articles/200348506-Using-the-Aardvark-adapter-with-a-Microwire-device
-- we are setting SPI Id = 1, since Id = 0 used for communication with memory
spi.setup(spiID, spi.MASTER, spi.CPOL_LOW, spi.CPHA_LOW, databits, clock_divider)
-- SPI Id=1 uses following pins https://nodemcu.readthedocs.io/en/master/modules/spi
-- Signal | IO index | ESP8266 pin
-- HSPI CLK | 5 | GPIO14
-- HSPI /CS | 8 | GPIO15
-- HSPI MOSI | 7 | GPIO13
-- HSPI MISO | 6 | GPIO12
-- Load Enable pin settings
-- note that it overwrite unused ChipSelect if pin=8, i.e. GPIO15
gpio.mode(microwire_LE_pin, gpio.OUTPUT)
gpio.write(microwire_LE_pin, gpio.LOW)
end
function microwire_send_data( data )
-- essentially send data via spi interface
-- and raise Load Enable pin for a bit (at least for 25 nS) at the end of transmission
-- first low LE pin, it should be low but just to be sure
gpio.write(microwire_LE_pin, gpio.LOW)
-- second send the data
local nBytes = spi.send(spiID, data)
-- finally raise LE pin for at least 25 ns,
-- note that it takes about 300 uS on ESP8266 before LE will be HIGH after spi.send
-- Note manual toggle like below is quite slow, the shortest duration is 160 uS
gpio.write(microwire_LE_pin, gpio.HIGH)
gpio.write(microwire_LE_pin, gpio.LOW)
end
microwire_setup_interface()
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