我正在尝试使用相同的 MISO、MOSI 和 CLOCK 引脚同时控制两个SPI设备，但使用不同的 SS 引脚。
一个是SparkFun的Wifly shield，它使用 SPI-to-UART 芯片，另一个是MAX31855。
他们独立工作，但不能一起工作。
下面列出了我正在使用的 SPI 到 UART 代码。我所做的唯一更改是在头文件中；我设置select()并deselect()公开。
#include "SpiUart.h"
// See section 8.10 of the datasheet for definitions
// of bits in the Enhanced Features Register (EFR)
#define EFR_ENABLE_CTS 1 << 7
#define EFR_ENABLE_RTS 1 << 6
#define EFR_ENABLE_ENHANCED_FUNCTIONS 1 << 4
// See section 8.4 of the datasheet for definitions
// of bits in the Line Control Register (LCR)
#define LCR_ENABLE_DIVISOR_LATCH 1 << 7
// The original crystal frequency used on the board (~12 MHz) didn't
// give a good range of baud rates so around July 2010 the crystal
// was replaced with a better frequency (~14 MHz).
#ifndef USE_14_MHZ_CRYSTAL
#define USE_14_MHZ_CRYSTAL true // true (14 MHz) , false (12 MHz)
#endif
#if USE_14_MHZ_CRYSTAL
#define XTAL_FREQUENCY 14745600UL // On-board crystal (New mid-2010 Version)
#else
#define XTAL_FREQUENCY 12288000UL // On-board crystal (Original Version)
#endif
// See datasheet section 7.8 for configuring the
// "Programmable baud rate generator"
#define PRESCALER 1 // Default prescaler after reset
#define BAUD_RATE_DIVISOR(baud) ((XTAL_FREQUENCY/PRESCALER)/(baud*16UL))
// TODO: Handle configuration better
// SC16IS750 register values
struct SPI_UART_cfg {
char DataFormat;
char Flow;
};
struct SPI_UART_cfg SPI_Uart_config = {
0x03,
// We need to enable flow control or we overflow buffers and
// lose data when used with the WiFly. Note that flow control
// needs to be enabled on the WiFly for this to work but it's
// possible to do that with flow control enabled here but not there.
// TODO: Make this able to be configured externally?
EFR_ENABLE_CTS | EFR_ENABLE_RTS | EFR_ENABLE_ENHANCED_FUNCTIONS
};
void SpiUartDevice::begin(unsigned long baudrate) {
/*
* Initialize SPI and UART communications
*
* Uses BAUD_RATE_DEFAULT as baudrate if none is given
*/
SPI.begin();
initUart(baudrate);
}
void SpiUartDevice::deselect() {
/*
* Deslects the SPI device
*/
digitalWrite(SS, HIGH);
}
void SpiUartDevice::select() {
/*
* Selects the SPI device
*/
digitalWrite(SS, LOW);
}
void SpiUartDevice::initUart(unsigned long baudrate) {
/*
* Initialise the UART.
*
* If initialisation fails this method does not return.
*/
// Initialise and test SC16IS750
configureUart(baudrate);
if(!uartConnected()){
while(1) {
// Lock up if we fail to initialise SPI UART bridge.
};
}
// The SPI UART bridge is now successfully initialised.
}
void SpiUartDevice::setBaudRate(unsigned long baudrate) {
unsigned long divisor = BAUD_RATE_DIVISOR(baudrate);
writeRegister(LCR, LCR_ENABLE_DIVISOR_LATCH); // "Program baudrate"
writeRegister(DLL, lowByte(divisor));
writeRegister(DLM, highByte(divisor));
}
void SpiUartDevice::configureUart(unsigned long baudrate) {
/*
* Configure the settings of the UART.
*/
// TODO: Improve with use of constants and calculations.
setBaudRate(baudrate);
writeRegister(LCR, 0xBF); // Access EFR register
writeRegister(EFR, SPI_Uart_config.Flow); // Enable enhanced registers
writeRegister(LCR, SPI_Uart_config.DataFormat); // 8 data bit, 1 stop bit, no parity
writeRegister(FCR, 0x06); // Reset TXFIFO, reset RXFIFO, non FIFO mode
writeRegister(FCR, 0x01); // Enable FIFO mode
}
boolean SpiUartDevice::uartConnected() {
/*
* Check that UART is connected and operational.
*/
// Perform read/write test to check if the UART is working
const char TEST_CHARACTER = 'H';
writeRegister(SPR, TEST_CHARACTER);
return (readRegister(SPR) == TEST_CHARACTER);
}
void SpiUartDevice::writeRegister(byte registerAddress, byte data) {
/*
* Write <data> byte to the SC16IS750 register <registerAddress>
*/
select();
SPI.transfer(registerAddress);
SPI.transfer(data);
deselect();
}
byte SpiUartDevice::readRegister(byte registerAddress) {
/*
* Read byte from SC16IS750 register at <registerAddress>.
*/
// Used in SPI read operations to flush slave's shift register
const byte SPI_DUMMY_BYTE = 0xFF;
char result;
select();
SPI.transfer(SPI_READ_MODE_FLAG | registerAddress);
result = SPI.transfer(SPI_DUMMY_BYTE);
deselect();
return result;
}
int SpiUartDevice::available() {
/*
* Get the number of bytes (characters) available for reading.
*
* This is data that's already arrived and stored in the receive
* buffer (which holds 64 bytes).
*/
// This alternative just checks if there's data but doesn't
// return how many characters are in the buffer:
// readRegister(LSR) & 0x01
return readRegister(RXLVL);
}
int SpiUartDevice::read() {
/*
* Read byte from UART.
*
* Returns byte read or or -1 if no data available.
*
* Acts in the same manner as 'Serial.read()'.
*/
if (!available()) {
return -1;
}
return readRegister(RHR);
}
size_t SpiUartDevice::write(byte value) {
/*
* Write byte to UART.
*/
while (readRegister(TXLVL) == 0) {
// Wait for space in TX buffer
};
writeRegister(THR, value);
}
size_t SpiUartDevice::write(const char *str, size_t size) {
/*
* Write string to UART.
*/
while (size--)
write(*str++);
while (readRegister(TXLVL) < 64) {
// Wait for empty TX buffer (slow).
// (But apparently still not slow enough to ensure delivery.)
};
}
void SpiUartDevice::flush() {
/*
* Flush characters from SC16IS750 receive buffer.
*/
// Note: This may not be the most appropriate flush approach.
// It might be better to just flush the UART's buffer
// rather than the buffer of the connected device
// which is essentially what this does.
while(available() > 0) {
read();
}
}
void SpiUartDevice::ioSetDirection(unsigned char bits) {
writeRegister(IODIR, bits);
}
void SpiUartDevice::ioSetState(unsigned char bits) {
writeRegister(IOSTATE, bits);
}
我试图这样使用它：
SpiSerial.deselect(); //Deselect Wi-Fi
delay(100); //Wait, just for the heck of it.
currentTemp = thermocouple.readFarenheit(); //Read from max31855... readFarenheit selects and unselects its own SS pin.
SpiSerial.select(); //Reselect Wi-Fi
但它仍然无法运行。为了让它发挥作用，我应该尝试什么进一步的事情？