Serial / UART decoder

Serial decoder

The Serial decoder sink decodes analog data on a serial bus to serial data. It can be used to monitor and analyze UART, RS232, RS485, MIDI, DMX or other compatible serial buses.

The serial decoder can monitor up to eight sources. When these sources are in sync (all sources are of one (combined) instrument), all captured data will be displayed in chronological order.

The sink uses a window for its output. The output can be saved to a text file.

Usage

Acquisition settings

For best results, use the following setups to capture the data:

Mode Sample frequency Pre-trigger Trigger timeout Trigger type Trigger level
Block 3 * baudrate 1 1% Infinite Rising/Falling 2 app. Mid level
Stream 3 * baudrate 1 - - - -
  1. The Serial decoder needs at least three times the baudrate to function. For proper function use always a multiple of the baudrate. (e.g. 4 or 5, don't use 3.5 or 4.5)
  2. If Type is set to normal use rising, if Type is set to inverted use falling.

Decoding serial buses

The serial decoder can be used to decode RS485, MIDI or DMX. See table below for settings:

Bus Baudrate Databits Parity Stopbits Type Midlevel
DMX 250000 8 none 2 Normal 1 Auto level
MIDI 31250 8 none 1 Normal Auto level
RS485 - - - - Normal 1 Auto level
  1. If measuring on the data+ of the differential bus use normal, if measuring on data- use inverted.

Serial decoder properties

To control the behavior of the Serial decoder sink, several properties are available. These can be accessed through a settings page in the output window.

Serial decoder - settings

The Source selector determines which source of the Serial decoder the settings page affects. The Default selection affects the set of properties that is used when a new source is connected to the Serial decoder.

Bitrate

For correct detection, the Bitrate property must be set to the correct value corresponding to the bus that is under measurement. It can be set to several common values, but also to an Auto detect value, where the Serial decoder will determine the used bitrate. It is also possible to enter an arbitrary value in the bitrate edit field.

Databits

For correct detection, the Databits property must be set to the correct number of data bits, corresponding to the bus that is under measurement. It can be set to several common values: 5, 6, 7 or 8 bits.

Parity

For correct detection, the Parity property must be set to the correct value, corresponding to the bus that is under measurement. It can be set to several common values: None, Odd, Even, Mark or Space.

Stopbits

For correct detection, the Stopbits property must be set to the correct value, corresponding to the bus that is under measurement. It can be set to two values: 1 or 2.

Type

For correct detection, the Type property must be set to the correct value, corresponding to the bus that is under measurement. It can be set to two values:

  • Normal levels above mid level are logic 0, levels below mid level are logic 1
  • Inverted levels above mid level are logic 1, levels below mid level are logic 0

Mid level

For correct detection, the Mid level property must be set to the correct value, corresponding to the bus that is under measurement. The default setting is Auto level.

Output window properties and actions

To control the behavior of the Serial decoder output window, properties and actions are available. These can be accessed through a toolbar with buttons at the top of the Serial decoder output window and through a popup menu which is shown when the sink is right clicked in the Object tree.

Serial decoder - data

Clear

The Clear action () clears the Serial decoder output window. The Clear action is available as button on the toolbar.

Auto scroll to bottom

The Auto scroll to bottom property () makes the Serial decoder output window scroll to the bottom of its content each time new data has arrived, making the latest data visible. The Auto scroll to bottom property is available as button on the toolbar.

Export data

The Export data action () saves the content of the Serial decoder output window to a text file. The Export data action is available as button on the toolbar.

Always on top

When the Always on top property () is switched on, the Serial decoder output window cannot be hidden under other windows of the Multi Channel oscilloscope software. The Always on top property is available as button on the toolbar and in the popup menu.

Common properties and actions

Related information

Gain / Offset

The Gain / Offset I/O multiplies a signal with a constant gain factor and adds a constant offset.

Limiter

The Limiter I/O limits or clips a signal to a certain range.