SPIWrite (Write to SPI Peripheral)
The SPIWrite instruction synchronously clocks out the specified number of bytes to the peripheral device. If the Source variable is type Long, the bytes are read from the most significant byte of the first element of the array first.
NOTE: Campbell Scientific documentation has been updated to replace legacy industry terms with modern terminology. Controller-peripheral are now used to describe SPI communications. The SPI controller initiates communications and makes requests of peripheral device(s). Peripheral devices process requests and return an appropriate response See https://www.oshwa.org/a-resolution-to-redefine-spi-signal-names for more information.
Syntax
SPIWrite ( BeginPort, Source, NumBytes )
Example
To demonstrate the operation of the SPI instructions to read an actual SPI device, the following describes reading an Analog Device ADXL350 3-axis accelerometer.
Since the device operates at 3.3V, all lines interfacing to the device must be set up accordingly. This device requires a Chip Select (CS) line to notify it of impending communication. Port C4 is used as the CS line.
'Declare Variables
Public Count as Long
Public id as long
Public D as Long
Public Dest(2) as Long
Public zero as Long
Dim pwr_ctrl as Long = {&H2D080000}
Dim bw_rate as Long = {&H2C060000}
Dim id_reg as Long = {&H80000000}
Dim Cfg as Long = {&H31000000}
Dim DReg as Long = {&HF2000000}
Public X as Long
Public Y as Long
Public Z as Long
BeginProg
PortPairConfig(C1,2) 'Configure C1/C2 as 3.3V
PortPairConfig(C3,2)'Configure C3/C4 as 3.3V
SPIOpen(C1,100000,&H60)'configure the SPI port for 100KHz operation with falling phase,
'low polarity, LSB first, 8 bit data.
PortSet(C4,0,1)'enable the CS
SPIWrite(C1,cfg,1)'write the data format register address
SPIWrite(C1,zero,1)'write the data format register with 0x0
PortSet(C4,1,1)
PortSet(C4,0,1)'enable the CS
SPIWrite(C1,id_reg,1)'write the id register address
SPIRead(C1,D,1)'read the id register
PortSet(C4,1,1)
movebytes(id,3,d,0,1)
PortSet(C4,0,1)'enable the CS
SPIWrite(C1,bw_rate,2)'Write the bwrate register with &H06
PortSet(C4,1,1)
PortSet(C4,0,1)'enable the CS
SPIWrite(C1,pwr_ctrl,2)'write the pwr_ctrl register with &H08
PortSet(C4,1,1)
Scan(1,sec,0,0)
Count += 1
PortSet(C4,0,1)
SPIWrite(C1,Dreg,1) 'send addr to read
SPIRead(C1,Dest,6) 'Read X, Y, and Z.
PortSet(C4,1,1)
movebytes(X,2,Dest,0,2) 'Move X into its own variable
movebytes(Y,2,Dest,2,2) 'Move Y into its own variable
movebytes(Z,2,Dest,4,2) 'Move Z into its own variable
NextScan
EndProg
Remarks
Serial Peripheral Interface (SPI) protocol is a clocked synchronous interface, used for short distance communication, generally between embedded devices.
Note that a prior understanding of the operation and details of the SPI protocol is assumed.
Parameters
BeginPort
The beginning port used for the three signals for SPI communications. The first port is the SPI clock signal. The next higher port from the clock port is the Controller Out Peripheral In (COPI) signal, and the next higher port is Controller In Peripheral Out (CIPO). BeginPort can be C1
Type: Constant
Source
The variable in which the bytes to be written are stored.
Type: Variable
NumBytes
The number of bytes that will be sent to the peripheral device.
Type: Variable or constant