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The USB can supply mA. In this case, this is enough to power the chip. The next step is to connect the clock signal. In some cases, it may also be called MOSI.
The final pin to connect is the Chip Select CS signal. In this application we only have a single chip, so connect CS0 directly to the chip CS pin. Please note that the chip select is active low, which means the chip enables communication when the signal is low and remains idle when the signal is high.
This is the default behavior of the NI USB, as well as the default for many devices on the market. Notice that there are two pins not connected in this case. For example, the HOLD pin can be used to pause serial communication without resetting the serial sequence.
NI USB-8451, Atmel AT25080A, and the LabVIEW SPI API
The complete functionality is usually atme, in the user manual of that particular device. The way you connect these pins also depends on the functionality. Keep in mind that the USB also has digital IO lines that can be used for this kind of application. Figure 2 shows the connection diagram atmmel you are using a single chip, however, one of the benefits of using the SPI communication bus is that it simplifies the connectivity and communication with many devices.
An example is shown in Figure 3.
ATMEL 25080NC SOP-8
If we are presented with this situation, we have two options to choose from. A second option is the use of another integrated circuit chip. Aatmel example, we can use a basic hex inverter as shown in Figure 4.
Basic Hex Inverter Chip.
It is important to input the chip select signal from the NI USB to the input of an inverter on the hex inverter chip e. This connection looks like Figure 5. Now we need to determine how to communicate to our device. In this case, reading and writing are different operations for the device. If this was an Analog to Digital Converter, an operation could be to set the voltage output.
We need a way to tell the device what operation we want to accomplish if we are writing or reading. This is done by using instructions. The product manual for this integrated circuit indicates the ATA uses an 8-bit instruction register. Figure 6 shows this instruction set. The instruction format is important to note as it indicates which instruction is being requested.
The instruction set shown in Figure 6 overviews three main features: The instruction set shows us how to format the instruction when we want to perform that operation. Referencing page seven of the ATA product manual, the most significant bit MSB is the first bit transmitted and received. It also mentions that once the ATA is selected with an active low chip select, the first byte is received thereafter.
This byte is the op-code that defines the operations to be performed. If we send an invalid op-code, no data is shifted into the ATA; data is not accepted via the SI pin, and the serial output pin SO remains in a high impedance state.
The device powers up in the write disable state when Vcc is applied. All programming instructions must therefore be preceded by a Write Enable instruction. The chip select also returns to an idle state high when the operation is complete. In order to program the ATA, two separate instructions must be executed. First, the device must be write enabled 250880 the WREN instruction. Also, the address of the memory location s to be programmed must be outside the protected address field location selected by the block write protection level.
During an internal write cycle, all commands are ignored except the RDSR instruction. For more information regarding the block write stmel and protected address fields, refer to the ATA product manual. A write instruction requires the following sequence.
Programming starts after the chip select pin is brought high. The low-to-high transition of the chip select pin must occur during the SCK low-time immediately after clocking in the D0 LSB data bit. Only the RDSR instruction is enabled during the write programming cycle. The ATA is capable of a byte page write operation.
After each byte of data is received, the five low-order address bits are internally incremented by one; the high-order bits of the address remain constant. If more than 32 bytes of data are transmitted, the address counter rolls over and the previously written data is overwritten. The ATA is automatically returned to the write disable state at the completion of a write cycle. For more information regarding the use of the status register, reference the ATA product manual. If the device is not write-enabled WRENthe device ignores the write instruction and returns to the standby state when chip select is brought high.
A new CS falling edge is required to reinitiate the serial communication. The SO line remains in a high impedance state throughout the operation. As with the other operations, the chip select finishes the operation by returning to an atmeo state high. After the chip select line is pulled low to select a device, the READ op-code is transmitted via the SI line followed by the byte address to be read A9-A0.
Upon completion, any data on the SI line is ignored. The data D7-D0 at the specified address is then shifted out onto the SO line.
If only one byte is read, the CS line should be driven high after the data comes out. The read sequence can be continued atmsl the byte address is automatically incremented and data continues to be shifted out. When the highest address is reached, the address counter rolls over to the lowest address allowing the entire memory to be read in one continuous read cycle. The ATA then provides the data requested by the byte address as defined in the functional description.
Note how the chip select returns to an idle state as it returns high. First we need to consider what we would like to do. Then we execute the script. You can review ztmel in the Overview of SPI tutorial linked at the bottom of this document. Referencing Figure 10, we can see the recommended clock frequencies given the voltage ranges. We are using Hz, which satisfies every range. It also switches all chip select pins from tristate to push-pull output driven high.
These VIs are shown in Figure This is typically done with the following VIs: This is covered in more detail in Scenario 3. The following sections cover three scenarios that overview LabVIEW and the different instructions we have discussed above in detail.
Referencing the timing diagram shown in Figure 7, we can see that we need to set the chip select low, provide the WREN hex instruction, and then reset the atmmel select high.
This process requires the use of three VIs: This scenario is a bit more advanced than the Set Write Enable Latch instruction.
In order to write data to the memory array, we need to enable the Set Write Enable Latch. This causes us to use the same VIs in Figure 14, as well as those required to write data to the atmle array.
The timing diagram in Figure 8 shows the need to set the chip select low, provide the WRITE hex instruction and byte address, and then the data to be written. Other functions are also used to create mock data to be written to the memory array.
This leaves us with the data to be written. As stated in the functional description, we are able to write up to 32 bytes of data. Atnel automatically create this by using a for loop and converting the iteration value to a byte and storing that value in a byte array.
NI USB, Atmel ATA, and the LabVIEW SPI API – National Instruments
This functionality is shown in Figure 15 note: The entire process to write data to the memory array consists of two instructions.
All of this interaction occurs on the SI line as shown in Figure The timing diagram for this instruction Figure 9 sets the chip select low then provides the READ hex instruction followed by the byte address to read. As we observed in Figure 16, we can overview the process of reading data from the memory array. This execution only requires one instruction. This is the only information sent on the SI line. The Basic API is another option to communicate with your chip.
The Basic API is useful if the operation of the chip involves user interaction. This may be a limitation when using loops or benchmarking a program with timers—the user has to wait until the entire program has completed on the NI USB until they see the timers update or the see the data. The downside is that sending these commands makes the Basic API less efficient.
When performance is critical, it is highly advised to use the Script API. The first step when using the Basic API is to set the chip select, clock rate, clock polarity, and clock phase. Figure 19 shows this simple configuration, and this should appear at the beginning of any Basic API program. Following the initial configuration, we can start programming our desired instruction.