RS232 communication - APC BR650MI - Page 1
Forum section: electronics / general

author: MartinFO
author_rank: Contributor
timestamp: August 27, 2025, 07:57:47 pm
content: HiI need to do a one-to-one replacement of an APC SU420 UPS to a APC BR650MI. The 420 has a DB9 serial connector, with the weird APC-pinout. I have successfully connected to this using the attached pin conversion (Baud 2400, 8bit), and got console access. The 420 is installed in an industrial application, which has this interface. The old 420 units are failing and I need to replace them with the newer BR650MI - but this have a RJ50 connection. It is supposed to be a USB/Serial combi port, with the pinout seen in the attachment. I have bought an adapter cable, with the connection seen in the attached diagram. I have confirmed this with a multimeter. This seem to adapt directly to a standard RS232 connection, but I cannot get a connection. I have also tried connecting to the RJ50 pins directly, similar to how the 420 adaption was made, but no luck. I can connect to PowerChute with USB with no problems, but I need console access via RS232. Does any of you have experience with this or ideas that could bring me further. APC tells me to use the USB cable:-).Thanks

author: asis
author_rank: Frequent Contributor
timestamp: August 28, 2025, 03:03:41 pm
content: Hi,In your UPS, in addition to the main MPU (ATMEL 89C51RC-UM IC11?) there should be another MPU (ARM STM32F103-C4 IC603?).IC11* ensures the operation of the entire control and monitoring circuit, including the inverter and switching relays.IC603* controls the control buttons, LCD, NMC (if available), USB and RS232 (MAX3232 IC601?)IC603*, as far as I understand, performs the function of the main communication adapter.IC603 ARM STM32F103-C4:pin 42 PORT- PA9 /TX , pin 43 PORT- PA10/RX are connected to the MPU (ATMEL 89C51RC-UM IC11?) pin 11 PORT- P3.0 /RXD , pin 13 PORT- P3.1/TXD.The main MPU status is read via this connection, SW is updated and calibration is performed.I assume that there is a technological connector J606 (RS232) pin1-(+5V); pin3-(TX); pin5-(TX), through which it is possible to communicate with the MPU (ATMEL 89C51RC-UM IC11?) via RS232.USB - pinout's = pin 44 PORT- PA11 /DM, pin 45 PORT- PA12/DP, which, accordingly, are output to the RJ50 connector.There is no USB Type A connector on the UPS case, so I cannot tell you which RJ50 contacts - you need to ring them.You did not explain how you connected to the UPS via USB and your pictures do not show this.Note that +5V power can be supplied from the PC side!IC603#pin 17 PORT- PA3/RX, pin 16 PORT- PA2/TX is connected to the (optional) NMC card connector. (probably SMBus)-pin 29 PORT- PB11/RX, pin 30 PORT- PB10/TX is connected to MAX3232 IC 601? pin11, pin12.TX / RX MAX3232 are output to the RJ50 connector - respectively pin's 2/TX, 8/RX, which corresponds to your pictures.Sorry, but I do not have a diagram and a photo of the PCB of your UPS and it is quite possible that I am wrong.-See this thread:https://www.eevblog.com/forum/repair/help-with-bricked-apc-ups-smt1500/

author: m k
author_rank: Super Contributor
timestamp: August 28, 2025, 04:09:04 pm
content: Your pin pictures are not clear, are they cable connection guides or signal naming guides.Cable must be so that transmitter goes to receiver.PC of today typically doesn't need those loops of old days.But if they are needed the 1-4 loop is incomplete, pin 6 is missing.Both cables are also missing that DB9 pin 6, is it for something special?Early UPS used very primitive system, there a simple signal level meant something.It's not very likely the same anymore, but who knows.Purpose of those loops is to tell old serial port controller that the connected device is active and ready.Generally those looped signals were used for hardware handshake and some controllers needed them all to be correctly signaled.DB9 pin 1 DCD is a pure modem thing, Data Carrier Detect, the phone is off hook and line is active.So if modem is not expected it has no meaning, maybe it should be pin 6 DSR.

author: darkspr1te
author_rank: Frequent Contributor
timestamp: August 29, 2025, 08:54:16 am
content: You may be getting your TX/RX mixed up, i would swap them and test again. (thats pins 2tx and 3rx)the diagrams do get confusing because it mentions DB9 without specifying which one so let me explainone cable is RJ50 to a DB9 and the DB9 pins are exposed as if they were a PC port and that is PIN 2 is TX and pin 3 RX and in order to connect to a pc DB9 you must use a null model cable to swap over TX and RX - this cable is common in old rack setups where they may have had a multiport serial over modem or multiport serial over ethernet for remote management via a dedicated link.Another cable mentioned by APC is the Direct to pc cable, This one has RJ50 on one end and a Female DB9 on the other and TX/RX are already swapped internally and is plugged direct on the PC serial port - this is the one you find often on amazonIf you look at the attached image, the port on the left side with pins is generally considered the PC side (or Terminal in old speak) which has TX on pin 2 and RX on pin 3,The port on the right side with holes and not pins is considered the modem side(Terminal equipment) and has RX on pin 2 and TX on pin 3I've also attach images of two newer APC cables , this is what is commonly sold by APC now the direct to pc port and extension cable (pass through no cross over no odd pinout) and you will note the RJ50 cable is configured as modem(holes).this should work with powerchute as well as UPSNUT or APCUPSD linux software for apc.

author: MartinFO
author_rank: Contributor
timestamp: August 29, 2025, 09:40:58 pm
content: Hi everyoneThanks for you replies. I got a little wiser today, which twists the whole question/issue a bit. I do not need serial connection - I thought so - but it turns out that the application uses the I/O's not serial. I just got a hold on the diagram of the installation.I have attached the diagram of the SU420's DB9 connector (IMG_4365), with the additional I/O functions. The application is connected the the UPS via a PLC. Pin 2 is connected to a PLC-input and is pulled HIGH (about 13V) when the UPS is in battery mode. This trigger a shut-down sequence. The PLC is also connected to Pin 1, where it via a relay pulls the pin HIGH (I think it is 24V), which shut down the UPS.For the BR650 I have found a similar diagram (for a CS500, but I think it can be used - CS500.png). I have confirmed the Pin 2 (ON_BATT) is HIGH (12V) when in battery module. I suppose Pin 8 (INVSD) is the Shutdown I/O (or I hope it is). I have tried supplying +5V from an external supply (common ground on pin 4 and pin 7 - tried both). No reaction. I wonder if the high level is 12V or more - the same pin is used as RX, which is higher - right? What do you think?I am sorry to flip to the topic - should I change the subject?

author: asis
author_rank: Frequent Contributor
timestamp: August 30, 2025, 03:35:07 am
content: Hi,A good practice would be to open the BR650 UPS case, write down the PCB type 640-xxxx, find out what MPUs are used and take a photo of the PCB and the connection to the RJ50.As far as I understand, you are dealing with a fifth-generation UPS and everything may not be as you imagine it now.If, as intended in the CS500, everything comes down to the Shut Down & Turn-on/Turn-of function, then I do not understand how the UPS is controlled via the RJ50 connector, which is labeled as USB & Serial.-During the period when I was doing repairs, I also failed to connect to the STM-series UPS via a null-modem cable.All that was available was to control via the NMC 9631 LAN Card.-I would like to offer some sketches from the APC STMxxx series.-Let the topic remain in place, we do not do repairs, we figure out how to connect the UPS.https://community.se.com/t5/Ask-the-Community/bd-p/ask-exchange-forum

author: MartinFO
author_rank: Contributor
timestamp: August 30, 2025, 08:10:42 am
content: I found this schematic online, but I cannot locate the RJ50 connector. Could there be an additional "connector-board"? It would seem the shut-down hardware it there.I will try to pull it apart and take some images later today.

author: MartinFO
author_rank: Contributor
timestamp: August 31, 2025, 06:21:10 pm
content: I took the UPS apart - here are some pictures of the board. I couldn't find the schematics, based on the part-no. I also max'ed out on attachement size, but top view is coming. I will try to back trace pin 8 and see if that gets me closer.

author: m k
author_rank: Super Contributor
timestamp: August 31, 2025, 06:58:24 pm
content: Left of the first picture seems to be a protection, right is where it happens.