3-wire serial bus interface

SPI has separate pins for input and output data, making it full-duplex. Some chips use a half-duplex interface similar to true SPI, but with a single data line. As an example, we have chosen to work with the National LM74 temperature sensor, whose pinout is shown below:.

The LM74's data sheet says that a complete transaction consists of 32 clock pulses. The LM74 will output data for the first 16 clocks, and will read input data for the remaining clocks. This sounds simple enough, but we need to setup our Aardvark adapter or Beagle analyzer properly to avoid damaging any devices. The key point to realize is that, although the Aardvark adapter will send out 4 MOSI bytes, the LM74 will only read the last 2 of these.

Add a comment. Active Oldest Votes. I would prefer I2C because speed doesn't matter in this scenario. The ATMega microcontroller has hardware peripherals for both methods so it's up to you. Hardwarefreak Hardwarefreak 1 1 silver badge 3 3 bronze badges. SPI is then much easier to debug because you don't need to deal with a protocol.

First, SS should be connected to ground, not power. Matt Young Matt Young You and Hardwarefreak responded simultaneously, but I found his answer to be a bit more complete. Many thanks again.

Chetan Bhargava Chetan Bhargava 4, 5 5 gold badges 25 25 silver badges 39 39 bronze badges. Although you didn't answer my question directly, your answer is an excellent supplement to the above answers. Extremely helpful. Helmuth R. Litfin Helmuth R. Litfin 41 3 3 bronze badges. Sign up or log in Sign up using Google. This exchange of data bits in microcontroller is done by some set of defined rules known as communication protocols.

Now if the data is sent in series i. More specifically, the data bits are transmitted one at a time in sequential manner over the data bus or communication channel in Serial Communication.

There are different types of data transfer available in the digital electronics such as serial communication and parallel communication. Similarly the protocols are divided into two types such as Serial Communication Protocol and Parallel Communication Protocols. In this article, the different types of Serial Communication Protocols will be discussed. Serial communication is the most widely used approach to transfer information between data processing peripherals.

The protocol is the secure and reliable form of communication having a set of rules addressed by the source host sender and destination host receiver similar to parallel communication. As already said above that in serial communication data is sent in the form of bits i.

There are several types of serial communication depending on the type of transmission mode and data transfer. In simplex method either of the medium i. So if the sender is transmitting the data then receiver can only accept and vice versa. So simplex method is one-way communication technique. The well-known examples of simplex method are Television and Radio.

In half duplex method both sender and receiver can be active but not at the same time. So if the sender is transmitting then receiver can accept but cannot send and similarly vice versa. The well-known examples of the half duplex is the internet where the user sends a request for a data and the gets it from server. In full duplex method, both receiver and transmitter can send data to each other at the same time. The well-known example is mobile phone.

Apart from this, for appropriate data transmission, the clock plays important role and it is one of the primary source. Malfunction of the clock results in unexpected data transmission even sometimes data loss. So, the clock synchronisation becomes very important when using serial communication. The clock is different for serial devices and it is classified in two type viz. It is a point-to-point connection from a master to slave. In this type of interface, all the devices use single CPU bus to share data and clock.

The data transmission becomes faster with same bus to share clock and data. Also there is no mismatch in baud rate in this interface. In transmitter side, there is a shift of the data onto serial line providing the clock as a separate signal as there is no start, stop and parity bits are added to data. SI is shifted in on the rising edge of SK. In some cases a 4. Or the device may send no start bit, just a variable length bit stream.

The minimum clock cycle time is 2uS, 1uS high and 1uS low. The clock speed is dependent on the microcontroller, typical speeds are 0Hz to kHz. Latest Posts. Problem migrating and fitting code from C Is XC16 not as good?