ZBasic System Library
208
ZBasic Microcontrollers
Type
Subroutine
Invocation
OpenSPISlave(flags)
Parameter
Method
Type
Description
flags
ByVal
integral
Flags controlling the SPI communication.
Discussion
This subroutine, available only for native mode devices, immediately activates the hardware SPI
controller in slave mode. The flags parameter specifies the characteristics of the SPI communication.
They must be set to be compatible with the SPI master with which you want to communicate. See the
table below for details.
SPI Slave Mode Configuration Bits
Function
Hex Value
Bit Mask
Clock Phase False
&H00
xx xx x0 xx
Clock Phase True
&H04
xx xx x1 xx
Clock Low at Idle
&H00
xx xx 0x xx
Clock High at Idle
&H08
xx xx 1x xx
Bit Order – MSB first
&H00
xx 0x xx xx
Bit Order – LSB first
&H20
xx 1x xx xx
For devices that have multiple SPI controllers (e.g. xmega-based devices), the most significant byte of the
flags parameter specifies the index of the SPI controller to use (0=PortD, 1=PortC, 2=PortE, 3=PortF).
See the tables below for information about which pins of each port are used for the SPI control/data pins.
The chip select pin for an SPI slave is a dedicated pin. See the Resource Usage sub-section SPI
Controllers for information about the available hardware SPI controllers for the various ZBasic devices
and the chip select, control and data pins for each. If you activate slave mode, you must also provide an
interrupt handler for the corresponding interrupt vector. While slave mode is active, SPICmd() calls are
ineffective for that channel. Slave mode can be canceled by calling CloseSPI().
See OpenSPI() for information about which pins are used for the data and control signals for each SPI
controller.
Note that the SPI master sets the SPI clock speed. The highest SPI clock speed that can be used
reliably is one quarter of the CPU clock speed of a ZX slave device. Depending on how much
computation the slave must perform to prepare data for sending back to the master, a substantially slower
SPI clock may need to be used. If a ZBasic device is being used as the master, it may be useful to set
the rxDelay parameter on calls to OpenSPI() on the master to allow additional processing time.
Compatibility
This subroutine is only supported for native mode devices.
See Also
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