diff options
Diffstat (limited to 'decoders/uart')
| -rw-r--r-- | decoders/uart/__init__.py | 93 | ||||
| -rw-r--r-- | decoders/uart/uart.py | 95 |
2 files changed, 93 insertions, 95 deletions
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: +[<packet-type>, <rxtx>, <packet-data>] + +This is the list of <packet-types>s and their respective <packet-data>: + - '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 <rxtx> field is 0 for RX packets, 1 for TX packets. +''' + from .uart import * diff --git a/decoders/uart/uart.py b/decoders/uart/uart.py index 5098977..4ceaef6 100644 --- a/decoders/uart/uart.py +++ b/decoders/uart/uart.py @@ -22,101 +22,6 @@ # UART protocol decoder # -# -# 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: -# [<packet-type>, <rxtx>, <packet-data>] -# -# This is the list of <packet-types>s and their respective <packet-data>: -# - '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 <rxtx> field is 0 for RX packets, 1 for TX packets. -# - import sigrokdecode as srd # States |