How to communicate with the Keysight 60501B Electronic Load module directly? - Page 1
Forum section: electronics / testgear

author: jgorsk
author_rank: Regular Contributor
timestamp: October 30, 2017, 12:20:53 pm
content: How to communicate with the Keysight 60501B (or similar) Electronic Load module over the serial link directly?Is the module using the same protocol as the Load Mainframe? What are Com port settings?Does anybody has a Load Mainframe that supports the 6050xB series load modules and couldhook up a scope to check the comms parameters?

author: jgorsk
author_rank: Regular Contributor
timestamp: November 03, 2017, 08:52:40 am
content: Does anybody have access to an Agilent/Keysight 6051A Load Mainframe and could do some simple oscilloscope measurements?The load modules have their own power supply and an insulated serial interface built in. If the communication protocolis known, they would be easy to use in a simple PC controlled electronic load.

author: samofab
author_rank: Regular Contributor
timestamp: November 03, 2017, 10:07:58 am
content: I have one open 6050A on my desk. Do you have specific measurement points?

author: AlfBaz
author_rank: Super Contributor
timestamp: November 03, 2017, 11:13:13 am
content: Do the free operating and programming manuals for your device, available from the keysight web site not provide the information you need?

author: jgorsk
author_rank: Regular Contributor
timestamp: November 03, 2017, 12:18:03 pm
content: There is no programming manual for the modules available. There is only a programming manual for the load mainframe.There are 3 connectors on top of each power module. Red IDC plugs are connected to them.The one closest to the mains transformer on the module carries 120/240Vac supply voltage.The connector on the other end of the module is for the RX/TX signals. It's the P3 connector.The connectors have 12 pins each, pin 1 is where the red wire on the ribbon cable is.P3.12 is the transmit signal from the module, P3.11 is the receive signal going to the module.Samofab, could you probe P3.11 on the red plug with reference to earth? You will need to slidethe white protective cover to the side slightly to access the contact. Can you figure out the parametersof the serial link? Speed, number of bits and so on? If that signal isn't Earth referenced you can useP2.8 (the middle connector) for ground. Before you do any oscilloscope measurements, please makesure you're probing the correct connectors. Avoid P1 (MAINS). I suggest you use a multimeter to makesure no mains is present on the contacts you're about to probe, that's for your safety.P3.12 is the standard serial TTL level UART signal (from the module), P3.11 is inverted TTL UART signal(to the module).Thanks for your help.

author: jgorsk
author_rank: Regular Contributor
timestamp: November 03, 2017, 03:51:52 pm
content: The schematics for the 60501B power module are at the end of this Service Manualhttp://literature.cdn.keysight.com/litweb/pdf/5951-2830.pdf

author: jgorsk
author_rank: Regular Contributor
timestamp: November 06, 2017, 10:20:37 am
content: Samofab, would you be able to probe the serial signals?

author: samofab
author_rank: Regular Contributor
timestamp: November 06, 2017, 08:18:14 pm
content: Sorry, this forum sometimes forgets to send notifications. I'll check signals tomorrow.

author: samofab
author_rank: Regular Contributor
timestamp: November 07, 2017, 11:08:15 am
content: Attachment of typical bus activity is here. Byte lasts about 144us, looks like 10 bits total.

author: samofab
author_rank: Regular Contributor
timestamp: November 07, 2017, 11:51:28 am
content: Bonus: open logic analyser (SUMP) captures of bus status at different operating points.SUMP also says that exact baud rate is 62713.

author: jgorsk
author_rank: Regular Contributor
timestamp: November 07, 2017, 12:30:12 pm
content: Thanks a lot for collecting the data. The speed is quite unusual. The protocol is most likely different than for the load mainframe.How do you view the Open Logic Analyser files?

author: samofab
author_rank: Regular Contributor
timestamp: November 07, 2017, 12:31:54 pm
content: One of the files attached is CSV for quick start.Otherwise download client software, I use this one:https://lxtreme.nl/projects/ols/Speed is close enough to 57600.. and it seems that only a byte or two are transferred together.. I guess it should work on 57600 reliably.

author: jgorsk
author_rank: Regular Contributor
timestamp: November 07, 2017, 01:00:49 pm
content: It doesn't work at 57600. 62300 seems like the correct speed. The module echoes back all data sent to it.The protocol is certainly different than for the Mainframe.

author: jgorsk
author_rank: Regular Contributor
timestamp: November 07, 2017, 01:12:20 pm
content: Samofab, could you capture the signal at power up? Since some data is being sent to the module constantly,it's hard to figure out what the protocol is. Hopefully different commands are sent at startupThanks again for your help

author: samofab
author_rank: Regular Contributor
timestamp: November 07, 2017, 07:26:49 pm
content: Open logic analyser is not exactly stellar in terms of triggering options... and I can't find a way to delay the trigger to the point where any meaningful module initialization happens.See attachment for rough view of the startup.

author: jgorsk
author_rank: Regular Contributor
timestamp: November 07, 2017, 08:06:20 pm
content: That unfortunately didn't work to well but there may be another solution.Luckily the signal to the module is inverted and should be properly receivedby RS232 RX port. Any chance you still have a PC with RS232 or a USB to RS232converter to make simple serial sniffer?

author: samofab
author_rank: Regular Contributor
timestamp: November 08, 2017, 12:30:10 pm
content: I attached RS232 adapter to the unit and turned it on (57600,n,8,1). The dump is in attachment. I don't think we'll be able to decode the protocol this way :-)... sorry

author: jgorsk
author_rank: Regular Contributor
timestamp: November 08, 2017, 03:14:09 pm
content: Thanks a lot for your effort Samofab. It is indeed hard to figure out the protocol details this way.I have a module on my desk. It doesn't communicate properly at 57600 but it seems to do at 62500,n,8,1.It echoes back all the data sent to it. it sends the responses at 62500. If I send data to it at 57600it responds with 'corrupted' data -different data than I send to it.If the comms are working you should see a lot of '0x27 0x00 0x00' in data in the streamsent to the module. I use Bray's terminal, you can set custom baud rate with ithttps://sites.google.com/site/terminalbpp/Can you give it another try at 62500bps please?

author: samofab
author_rank: Regular Contributor
timestamp: November 08, 2017, 03:39:18 pm
content: Last try (6050A takes a lot of space).The data looks good now - I made a few commands, hope something changed in datastream.Nice software terminalbpp!

author: samofab
author_rank: Regular Contributor
timestamp: November 08, 2017, 08:50:15 pm
content: PS: the reason why my 6050A was on my desk was repair of ebay sourced 60501B module. The seller had 3 for parts units. My unit had a broken transformer - it's likely that others have the same error. There's still one module available from this seller for a bargain (no affiliation).I am at a loss how transformer failed. All wingdings had a short. Lived my whole life under the impression that transformers are something that never fails if fused.

author: jgorsk
author_rank: Regular Contributor
timestamp: November 09, 2017, 09:26:32 am
content: Thank you so much for collecting the data. I have something to work with.Believe it or not, I bought the first one of the 3 faulty 60501B on ebay. It had 3 blown fuses and a faulty transformer.I have no idea how it failed either. It has very low inductance of the primary windings. Maybe something happenedto the core? I've seen another case similar to that. The primary windings were perfectly fine but they had very lowinductance. The core somehow lost it's magnetic properties. It was a toroidal core though.I couldn't find a direct replacement for the transformer but this may work with some small modifications to the boardhttp://www.brevetrafo.com/catalog/transformers-for-pcb/tez-p119.htmlTEZ16/D230/15-15VYou can buy it herehttps://www.tme.eu/gb/details/tez16_d_15-15v/pcb-transformers/breve-tufvassons/tez16d23015-15v/The shape is similar to the original one but the pinout is different.

author: jgorsk
author_rank: Regular Contributor
timestamp: April 13, 2018, 08:11:42 am
content: Only a very basic protocol is implemented in the 60501B load module. It allows writing directly to the DACs, I/O registers, variables and reading variables.It's still usable but not very convenient.