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IEN1 = 0x04; /. enable spi interrupt./ SPCON = 0x40; /. spi run./ transmitcompleted = 0; /. clear software transfert flag./ EA=1; /. enable interrupts./ while(1) /. endless./ if(transmitcompleted) SPDAT = serialdata; /. echo data to master./.
I have a custom board using BF-547 and serial SPI flash 'AT45DB641E'. I use ICE-1000 via the JTAG port for debugging currently. I want to use the SPI PROM attached to the DSP. I have created the appropriate loader file using the tool. However, when I try to program the device, I am unable to get the driver file for the SPI flash.
When operating in Master mode, the SPI peripherals gen erate a serial clock and data to the slave device that needs to be accessed. The SPI peripherals can generate the serial clock from 390 KHz to 50 MHz by dividing the MSS clock, which can be controlled by software. The peripheral DMA (PDMA) in the MSS.

Serial Peripheral Interface (SPI) is an interface bus commonly used to send data between microcontrollers and small peripherals such as shift registers, sensors, and SD cards. It uses separate clock and data lines, along with a select line to choose the device you wish to talk to.

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Introduction

Serial Peripheral Interface (SPI) is an interface bus commonly used to send data between microcontrollers and small peripherals such as shift registers, sensors, and SD cards. It uses separate clock and data lines, along with a select line to choose the device you wish to talk to.

Suggested Reading

Stuff that would be helpful to know before reading this tutorial:

Serial Communication

Asynchronous serial communication concepts: packets, signal levels, baud rates, UARTs and more!

Binary

Binary is the numeral system of electronics and programming...so it must be important to learn. But, what is binary? How does it translate to other numeral systems like decimal?

Shift Registers

An introduction to shift registers and potential uses.

Logic Levels

Learn the difference between 3.3V and 5V devices and logic levels.

What's Wrong with Serial Ports?

A common serial port, the kind with TX and RX lines, is called 'asynchronous' (not synchronous) because there is no control over when data is sent or any guarantee that both sides are running at precisely the same rate. Since computers normally rely on everything being synchronized to a single “clock” (the main crystal attached to a computer that drives everything), this can be a problem when two systems with slightly different clocks try to communicate with each other.

To work around this problem, asynchronous serial connections add extra start and stop bits to each byte help the receiver sync up to data as it arrives. Both sides must also agree on the transmission speed (such as 9600 bits per second) in advance. Slight differences in the transmission rate aren't a problem because the receiver re-syncs at the start of each byte.

(By the way, if you noticed that '11001010' does not equal 0x53 in the above diagram, kudos to your attention to detail. Serial protocols will often send the least significant bits first, so the smallest bit is on the far left. The lower nybble is actually 0011 = 0x3, and the upper nybble is 0101 = 0x5.)

Asynchronous serial works just fine, but has a lot of overhead in both the extra start and stop bits sent with every byte, and the complex hardware required to send and receive data. And as you've probably noticed in your own projects, if both sides aren't set to the same speed, the received data will be garbage. This is because the receiver is sampling the bits at very specific times (the arrows in the above diagram). If the receiver is looking at the wrong times, it will see the wrong bits.

A Synchronous Solution

SPI works in a slightly different manner. It's a 'synchronous' data bus, which means that it uses separate lines for data and a 'clock' that keeps both sides in perfect sync. The clock is an oscillating signal that tells the receiver exactly when to sample the bits on the data line. This could be the rising (low to high) or falling (high to low) edge of the clock signal; the datasheet will specify which one to use. When the receiver detects that edge, it will immediately look at the data line to read the next bit (see the arrows in the below diagram). Because the clock is sent along with the data, specifying the speed isn't important, although devices will have a top speed at which they can operate (We'll discuss choosing the proper clock edge and speed in a bit).

One reason that SPI is so popular is that the receiving hardware can be a simple shift register. This is a much simpler (and cheaper!) piece of hardware than the full-up UART (Universal Asynchronous Receiver / Transmitter) that asynchronous serial requires.

Receiving Data

Note: You may not recognize the COPI/CIPO labels for SPI pins. SparkFun has joined with other members of OSHWA in a resolution to move away from using 'Master' and 'Slave' to describe signals between the controller and the peripheral. Check out this page for more on our reasoning behind this change. You can also see OSHWA's resolution here.

You might be thinking to yourself, self, that sounds great for one-way communications, but how do you send data back in the opposite direction? Here's where things get slightly more complicated.

In SPI, only one side generates the clock signal (usually called CLK or SCK for Serial ClocK). The side that generates the clock is called the 'controller', and the other side is called the 'peripheral'. There is always only one controller (which is almost always your microcontroller), but there can be multiple peripherals (more on this in a bit).

When data is sent from the controller to a peripheral, it's sent on a data line called COPI, for 'Controller Out / Peripheral In'. If the peripheral needs to send a response back to the controller, the controller will continue to generate a prearranged number of clock cycles, and the peripheral will put the data onto a third data line called CIPO, for 'Controller In / Peripheral Out'.

Notice we said 'prearranged' in the above description. Because the controller always generates the clock signal, it must know in advance when a peripheral needs to return data and how much data will be returned. This is very different than asynchronous serial, where random amounts of data can be sent in either direction at any time. In practice this isn't a problem, as SPI is generally used to talk to sensors that have a very specific command structure. For example, if you send the command for 'read data' to a device, you know that the device will always send you, for example, two bytes in return. (In cases where you might want to return a variable amount of data, you could always return one or two bytes specifying the length of the data and then have the controller retrieve the full amount.)

Note that SPI is 'full duplex' (has separate send and receive lines), and, thus, in certain situations, you can transmit and receive data at the same time (for example, requesting a new sensor reading while retrieving the data from the previous one). Your device's datasheet will tell you if this is possible.

Chip Select (CS)

There's one last line you should be aware of, called CS for Chip Select. This tells the peripheral that it should wake up and receive / send data and is also used when multiple peripherals are present to select the one you'd like to talk to.

The CS line is normally held high, which disconnects the peripheral from the SPI bus. (This type of logic is known as “active low,” and you’ll often see used it for enable and reset lines.) Just before data is sent to the peripheral, the line is brought low, which activates the peripheral. When you're done using the peripheral, the line is made high again. In a shift register, this corresponds to the 'latch' input, which transfers the received data to the output lines.

Multiple peripherals

There are two ways of connecting multiple peripherals to an SPI bus:

In general, each peripheral will need a separate CS line. To talk to a particular peripheral, you'll make that peripheral's CS line low and keep the rest of them high (you don't want two peripherals activated at the same time, or they may both try to talk on the same CIPO line resulting in garbled data). Lots of peripherals will require lots of CS lines; if you're running low on outputs, there are binary decoder chips that can multiply your CS outputs.

On the other hand, some parts prefer to be daisy-chained together, with the CIPO (output) of one going to the COPI (input) of the next. In this case, a single CS line goes to all the peripherals. Once all the data is sent, the CS line is raised, w

Serial Program Ing (spi) Enable