X-Git-Url: https://sigrok.org/gitweb/?p=libsigrokdecode.git;a=blobdiff_plain;f=decoders%2Fuart%2F__init__.py;h=1c7f317841622edc11de5405305f6892af0d7624;hp=4267d83b915acc688da19e171d4313baed8b379b;hb=8e828d2a29154fb9cae8c9c38d27c60f820dd584;hpb=1ccef4616d2c6d6fcdfee6a72d051387625678ca diff --git a/decoders/uart/__init__.py b/decoders/uart/__init__.py index 4267d83..1c7f317 100644 --- a/decoders/uart/__init__.py +++ b/decoders/uart/__init__.py @@ -18,5 +18,98 @@ ## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA ## +''' +Universal Asynchronous Receiver Transmitter (UART) is a simple serial +communication protocol which allows two devices to talk to each other. + +It uses just two data signals and a ground (GND) signal: + - RX/RXD: Receive signal + - TX/TXD: Transmit signal + +The protocol is asynchronous, i.e., there is no dedicated clock signal. +Rather, both devices have to agree on a baudrate (number of bits to be +transmitted per second) beforehand. Baudrates can be arbitrary in theory, +but usually the choice is limited by the hardware UARTs that are used. +Common values are 9600 or 115200. + +The protocol allows full-duplex transmission, i.e. both devices can send +data at the same time. However, unlike SPI (which is always full-duplex, +i.e., each send operation is automatically also a receive operation), UART +allows one-way communication, too. In such a case only one signal (and GND) +is required. + +The data is sent over the TX line in so-called 'frames', which consist of: + - Exactly one start bit (always 0/low). + - Between 5 and 9 data bits. + - An (optional) parity bit. + - One or more stop bit(s). + +The idle state of the RX/TX line is 1/high. As the start bit is 0/low, the +receiver can continually monitor its RX line for a falling edge, in order +to detect the start bit. + +Once detected, it can (due to the agreed-upon baudrate and thus the known +width/duration of one UART bit) sample the state of the RX line "in the +middle" of each (start/data/parity/stop) bit it wants to analyze. + +It is configurable whether there is a parity bit in a frame, and if yes, +which type of parity is used: + - None: No parity bit is included. + - Odd: The number of 1 bits in the data (and parity bit itself) is odd. + - Even: The number of 1 bits in the data (and parity bit itself) is even. + - Mark/one: The parity bit is always 1/high (also called 'mark state'). + - Space/zero: The parity bit is always 0/low (also called 'space state'). + +It is also configurable how many stop bits are to be used: + - 1 stop bit (most common case) + - 2 stop bits + - 1.5 stop bits (i.e., one stop bit, but 1.5 times the UART bit width) + - 0.5 stop bits (i.e., one stop bit, but 0.5 times the UART bit width) + +The bit order of the 5-9 data bits is LSB-first. + +Possible special cases: + - One or both data lines could be inverted, which also means that the idle + state of the signal line(s) is low instead of high. + - Only the data bits on one or both data lines (and the parity bit) could + be inverted (but the start/stop bits remain non-inverted). + - The bit order could be MSB-first instead of LSB-first. + - The baudrate could change in the middle of the communication. This only + happens in very special cases, and can only work if both devices know + to which baudrate they are to switch, and when. + - Theoretically, the baudrate on RX and the one on TX could also be + different, but that's a very obscure case and probably doesn't happen + very often in practice. + +Error conditions: + - If there is a parity bit, but it doesn't match the expected parity, + this is called a 'parity error'. + - If there are no stop bit(s), that's called a 'frame error'. + +More information: +TODO: URLs + +Protocol output format: + +UART packet: +[, , ] + +This is the list of s and their respective : + - 'STARTBIT': The data is the (integer) value of the start bit (0 or 1). + - 'DATA': The data is the (integer) value of the UART data. Valid values + range from 0 to 512 (as the data can be up to 9 bits in size). + - 'PARITYBIT': The data is the (integer) value of the parity bit (0 or 1). + - 'STOPBIT': The data is the (integer) value of the stop bit (0 or 1). + - 'INVALID STARTBIT': The data is the (integer) value of the start bit + (0 or 1). + - 'INVALID STOPBIT': The data is the (integer) value of the stop bit + (0 or 1). + - 'PARITY ERROR': The data is a tuple with two entries. The first one is + the expected parity value, the second is the actual parity value. + - TODO: Frame error? + +The field is 0 for RX packets, 1 for TX packets. +''' + from .uart import *