Bailey O.H.Embedded systems.Desktop integration.2005

**********************************************************************************/

//Output sizeof(txBuf) characters to I2C SlaveID 0x50 in a complete

//Data Transfer

I2Cm_1_bWriteCBytes(0x50, txBuf, sizeof(txBuf), I2Cm_1_CompleteXfer);

}

Two function calls are all that is required to send data via I2C. Next we will examine the 1-Wire interface used for collecting the temperature. Before we do, be aware that the 1-Wire user module is a third-party module. It can be downloaded from www.psocdeveloper.com and is included with the source files for this book, available at www.wordware.com/files/embsys and www.time-lines.com.

Adding User Modules to the PSoC Designer

To add the 1-Wire module simply copy the entire data directory to the C:\Program Files\Cypress MicroSystems\PSoC Designer\ Data folder. If you have the PSoC Designer open, close it and restart it; you should now see the 1-Wire user modules under the Digital Comm button.

The PSoC 1-Wire Interface

Next we have the 1-Wire interface to implement. Much of the work in implementation has been done in the Designer, so we need to add the code to address the 1-Wire devices. There are more functions available for the 1-Wire, so instead of going through them all we will only list those that are needed for our device. They are:

our prototype for the design. Having said that we will now explore the SPI master user module as it relates to our needs.

There are just a few API calls available in the SPIM user module. They are:

SPIM_Start — Configures the SPI mode and sets the proper bits in the control registers

SPIM_Start — Disables the SPI interface by clearing the enable bit in the control register

SPIM_EnableInt — Enables the SP interrupt on an SPI done condition

SPIM_DisableInt — Disables the SPI interrupt on an SPI done condition

SPIM_SendTxData — Transmits a byte to slave device

SPIM_bReadRxData — Returns a received byte from a slave device

SPIM_bReadStatus — Returns the contents of the control/status register

As always, the slave’s device signal must be asserted to a low state just before sending data. The RX Buffer full flag should be checked prior to a call to SPIM_bReadRxData to verify data has been received. The following listing sends the message “Hello from PSoC” to an SPI slave device.

Listing 10-3

/********************************************************************************* Send "Hello from PSoC" to SPI Device

**********************************************************************************/

//Start the SPI interface with control mode 0 ans MSB First SPIM_1_Start(SPIM_1_SPIM_MODE_0 || SPIM_1_SPIM_MSB_FIRST);

//While there are still valid characters, loop

while (*ptrSPI_MSG !=0) {

// Check RX Buffer and TX Data Buffer

while(! (SPIM_1_bReadStatus() & SPIM_1_SPIM_TX_BUFFER_EMPTY)){;} // Send next byte

424Chapter 10 / The PSoC Prototype

UART_cGetChar — Receives character from RX data register when available

UART_Write — Transmits multiple characters to TX port

UART_CWrite — Transmits multiple constant characters to TX port

UART_cReadChar — Does immediate receive from RX port; returns either valid ASCII character or zero if no character is available

UART_iReadChar — Same as above but returns 2 bytes, one with ASCII character and other with any error code or zero if no error detected

UART_PutCRLF — Sends carriage return and line feed to TX port

There are several other high-level commands that deal with command buffer status and the transmission of hex data we will not be using. In addition, there are several low-level API functions we will be using. They are:

UART_Start — Enables UART user module

UART_Stop — Disables UART user module

Again, there are several other commands that deal with interrupts and register status that we will not be discussing at this time. Let’s take a look at what is required to send the infamous “Hello from PSoC” message via the UART.

The UART divides the clock source by 8, which means we need a clock that is eight times the desired baud rate. The simplest method of implementing a clock is to use a Counter8 user module as a source. This, however, is not the only way to attain a clock source, but for the purpose of our listing we will assume a Counter8 clock is being used for our UART with a device clock speed of 24 mHz. The Counter8 parameters would be set as follows:

Clock — 24 mHz

Enable — High

Output — None

Period — 155

CompareValue — 78

CompareType — Less than or equal

InterruptType — Terminal count

Using the above parameters we would calculate the UART baud rate as:

BaudRate = 24,000,000/((155 + 1) * 8) = 19.2K baud

Pay close attention to variables in the preceding equation. If you change the clock speed you will also change the baud rate, so keep this in mind when determining the PSoC main clock rate.

Using the above calculations we would set the UART user module parameters as follows:

We are using the broadcast line from the Counter8 user module as the clock source for the UART user module. The RX in is attached to the UART global input and the TX out is attached to the UART global output line. We are using an interrupt triggered on a transmit or receive complete. In order to use this mode the

428 Chapter 10 / The PSoC Prototype

ptrSPI_MSG++;

}

/********************************************************************************* Send "Hello from PSoC" from the UART

**********************************************************************************/

// The following is a method of configuring the Counter8 user module in code. /*********************************************************************************

*********************************************************************************/

// Send string

UART_1_CPutString("\r\nHello from PSoCb\r\n");

}

Before we conclude with the PSoC device, please spend some time getting familiar with how this device works and the procedures to configure and program it. The PSoC really represents a convergence of software and hardware in developing a hardware component. There is no way possible to cover the capabilities of this product in the space of this book. The idea is to provide you with the information needed to understand and start using the device in an intelligent fashion. If you’re new to electronics I do not recommend using this device until you’ve built several circuits using the BASIC Stamp or PIC components.