Siglent SDS2104X Plus - serial decoding digital input - number of bits - Page 1
Forum section: electronics / testgear

author: Sorama
author_rank: Frequent Contributor
timestamp: December 16, 2024, 03:35:34 pm
content: @tautech and all other respected Siglent boysWhen using the digital inputs with the optional probe of a Siglent scope 2000X plus series; how should I interpret the Bus Wide of the parameter 'Bus'?Is this the number of bits including Start/Stop/Parity?So let's say my bus is using 11 bits (9 data, 1 start, 1 stop bit): should I put the Bus Wide (strange word, no?) at 11?I'm using a ninth bit for addressing between a processor (Dallas 80C52 compatible) and multiple slaves using UART (RS485 transceivers).However, when doing so, the decoding is not correct.However I set it, decoding is not correct.tnx.Sam

author: tautech
author_rank: Super Contributor
timestamp: December 17, 2024, 12:35:27 am
content: Onemustask what firmware version is in use ?Latest is V1.6.2R5

author: Sorama
author_rank: Frequent Contributor
timestamp: December 17, 2024, 05:44:56 am
content: Latest it is.Tnx.

author: 2N3055
author_rank: Super Contributor
timestamp: December 17, 2024, 08:31:53 am
content: Serial protocols have no parallel number of bits, hence serial.For serial UART type protocols we are looking into single bit that changes in time.You set up parameters in UART Config. Baud rate, data length, parity and number of stop bits. Idle level and bit order.Select which digital input pin or analog channel you are decoding.And, at this time, UART decoders form Siglent does not support 9 bit modes with addressing.

author: Sorama
author_rank: Frequent Contributor
timestamp: December 17, 2024, 09:14:37 am
content: tnx.I am (of course) not confusing parallel with serial: I just mentioned the setting on the Siglent scope in Digital Bus Menu (see screenshot) which asks for "Bit Wide".What is one supposed to put in there?You say 9 bit is not supported, but the fact you can define parity to Mark or Space, that is supposed to be the implementation of 9 bit decoding.That is how the other manufacturers do and they specifically mention it for 9 bit multidrop systems with the 9th bit set to 1 when an address byte is sent.So, are you sure the Siglent cannot handle it?PS: the screenshot shows the TTL levels of a RS485 transceiver running @ 345600 baud where Di is the driver/sender and coming from a 80c52 processor.Protocol= when 9th bit is set to 1, the frame is considered to be an address of a slave.The green trace is the sending of the address byte (9 bits, 1 start and 1 stop) but doesn't get decoded correctly.The red trace is the receiver, a slave that is answering.As you may not be able to see; the triggering is not stable; there is a horizontal jitter all the time that impacts a correct decoding. But as said before, I can't get it right even with correct holdoff time.If you have a suggestion to solve that, please do so.tnx again.

author: 2N3055
author_rank: Super Contributor
timestamp: December 17, 2024, 02:52:06 pm
content: Quote from: Sorama on December 17, 2024, 09:14:37 amOk.Digital probe supports 16bit wide input. In 2 groups of 8 bits.In digital setup you can enable/disable individual bits.You can enable only 1 bit if you want to.You will generally enable only input bits you need.Whatever you set in digital input settings is irrelevant to serial UART decode option.In fact, you need to disable Digital bus display. It is not meant for this, but for decoding digital bus parallel values.In serial UART decode options you need to set up what scope input will be source of data for RX and TX.It can be analog or digital inputs.Yes, unfortunately, I am sure that UART decode/trigger currently does not support addressed 9 bit mode.As for the trigger, I can't say much with the data I have.You cannot trigger from protocol, because 9bit is not supported.You can use standard edge trigger with holdoff, or one of pulse triggers, with or without holdoff.Make sure that levels for digital probe are set correctly for your signal.

author: Sorama
author_rank: Frequent Contributor
timestamp: December 17, 2024, 06:24:32 pm
content: Tnx.Now that I have your attention 😃 …I know you are close to Siglent, so if there is something like a feature request list, feel free to put 9 bit serial decoding on it.Secondly -I know I am asking a lot -but if you could shine your light on my other topic that is related to serial decoding and terminology, I would be very grateful again:https://www.eevblog.com/forum/chat/terminology-wrt-uart-active-low-(magnova)-vs-idle-low-(siglent)/Sam

author: 2N3055
author_rank: Super Contributor
timestamp: December 17, 2024, 06:42:48 pm
content: Quote from: Sorama on December 17, 2024, 06:24:32 pmYou are late to the party. I already asked for it.I personally stumbled upon this myself.I cannot deny nor confirm if it will be added or if it will, when.Same as you, I can only report, someone else is making decision.Will take a look at that other topic...Best,

author: Sorama
author_rank: Frequent Contributor
timestamp: December 18, 2024, 07:48:05 am
content: if the Siglent does not support 9 bit serial decoding, I still wonder how to interpret this (extract from the user manual of SDS200X Plus):

author: 2N3055
author_rank: Super Contributor
timestamp: December 18, 2024, 08:38:35 am
content: Quote from: Sorama on December 18, 2024, 07:48:05 amWhat you show is exactly explanation that it does not work.It tells you what erroneous interpretation will happen if you try decoding 9 bit protocol.It will wrongly think it is a parity or extra stop bit.