Question: Do Acromag’s 9xxMB Modbus-RTU I/O modules work with leased-line modems?

Answer: Yes. However, it may depend on the type/brand of modem and software being used. Acromag has performed in-house testing at 9600 baud with the Multi-tech MT5634ZBA modems and the Model 913MB-0900. See below for set up and conclusions:

PC Operating System: Windows ME

PC Serial Port Configuration: Using Device Manager, set the port to 9600 baud, 8 data bits, 2 stop bits, no parity, and no flow control. Under the Advanced Tab, set FIFO buffers (checkbox) enabled and transmit/receive buffers (slidebars) as low as possible.

Leased Line Modems: Multitech – Model MT5634ZBA

AT Commands and Configuration for both modems (host and remote location):

&f: Factory Default

&d0: Ignore DTR

&K0: Disable Flow Control

\j0: Serial port speed is independent of connection speed

\n0: disable error correction

%c0: disable data compression

%e0: disable fallback

s37: talk between modems at 9600 baud

$sb9600: serial port at 9600 baud

$eb1: set modem up for 11 bit word

#p0: set parity to none

&w: SAVE

RS232/422-485 Converter at Remote Location: B&B Electronics Model 485BAT3. The two switches are set to RS485 and Echo off. You’ll need to jumper the TxD (B) with the RxD(B) together. You’ll also need to jumper the TxD(A) and RxD(A) lines together. The TxD(B) line is wired to the D terminal on the 913MB and the TxD(A) line is wired to the D(bar) terminal on the 913MB.

Acromag 9xxMB I/O Module: Model 913MB-0900 (4ch AI-I, plus 4ch DO). Settings were address 247, 9600 baud, 8 databits, 2 stop bits, no parity

Validation Software Used (two packages):
Acromag Configuration Software 9500-200B
Com Debug by Windmill Software www.windmill.co.uk

Results/Summary: Windmill Software’s ComDebug was able to issue/receive commands and responses from the 913MB reliably. Also, Acromag’s 9500-200B software was able to upload and poll the 913MB module reliably. However, the 9500-200B software was not able to download a configuration to the 913MB. Since the 9500-200B Configuration Software Package is truly intended to configure modules locally from a PC or Notebook computer workstation and not over network connections, this was deemed okay. Ultimately, the successful and reliable polling of both the Windmill Software and 9500-200B Configuration Software indicates standard software packages intended for this applications (ie; HMI’s such as Wonderware, Intellution, Citect, etc…) should work well.