Regarding stop bits of the HDPM6000

[Miyai]

Hello,

Can HDPM6000 support communication specification of stop bit 1?
I would like to integrate this into our existing 8N1 network system.

I found following in Schneider's FAQ. I also checked the HDPM6000's web browser,
but I couldn't change the parity and stop bits.

https://www.se.com/us/en/faqs/FAQ000258271/

Regards,

Miyai

[Mehran_Mehrnia]

Hi @Miyai 

As mentioned in that FAQ, the default serial port settings are listed below, and some of them cannot be configured through the webpage. The meter also supports 8N1.

Default serial settings:

• Unit ID: 1
• Parity: None
• Stop Bits: 2
• Baud Rate: 115200

Best Regards,

-Mehran

L3 Expert Advanced metering

[Miyai]

Hi, @Mehran_Mehrnia 

If master unit is set to 8N1, will the HDPM6000 slave unit's setting automatically switch from 8N2 to 8N1?

Generally, I think that mismatches between the 8N1 and 8N2 settings would result in communication problems, but can the HDPM6000 automatically detect this?

Best regards,

Miyai

[Mehran_Mehrnia]

Hi  @Miyai 

The HDPM6000 does not change its stop‑bit configuration. It always operates as 8‑N‑2.

However, Modbus RTU includes a required idle‑line silence between characters that is longer than a single stop bit. Because the UART only checks that the line is HIGH at the stop‑bit sampling moment, not for the full programmed stop‑bit duration, the meter can accept the master’s 8‑N‑1 transmission even though it expects 8‑N‑2.

In other words, the meter is not switching its configuration; the additional idle time on the bus makes the mismatch appear compatible. It usually works because UART receivers accept any stop period that remains HIGH at the sampling point, and Modbus RTU enforces sufficiently long silent gaps. As a result, the bus stays in the idle HIGH state for longer than both the 1‑stop‑bit and 2‑stop‑bit durations, so the slave UART effectively “sees” enough stop‑bit time even though the master only transmitted one. 

However, at higher baud rates, on noisy RS‑485 lines, or in systems with tighter timing tolerances, this mismatch may cause intermittent framing errors.

Best Regards,

-Mehran

L3 Expert Advanced metering

[Mehran_Mehrnia · Accepted solution]

Hi  @Miyai 

Following my previous comment, and as verified by the hardware team, the true default serial setting for the HDPM6000 is 8N1.

As mentioned previously, the HDPM6000 uses the UART driver built into the communications processor. On receive, it never checks for a second stop bit, so it can successfully receive data whether the sender uses one or two stop bits.

The meter is also configured to transmit with only one stop bit. As a result, communication with a polling device configured for 8N2 depends on whether that device strictly requires a full two‑stop‑bit duration for valid reception, or whether it samples only the first stop bit as UARTs typically sample the stop bit once and Modbus RTU provides long idle gaps between characters, the receiver still sees enough HIGH idle time to treat the frame as valid.

The HDPM6000 default serial port settings FAQ will be corrected as:

Unit ID - 1
Parity - None
Stop Bits - 1
Baud Rate - 115200

Best Regards,

-Mehran

L3 Expert Advanced metering