Avatar of mrsisti

asked on 

detecting connectivity betweend pc and modem using mscomm and only 3 wire rs232

I have to be able to detect the loss of connection with a device but it has no CD or RTS CTS DTR DSR RI

i only have a transmit and receive and ground

I have to be able to detect the fact that has lost physical connection.

Networking Hardware-OtherVisual Basic.NET

Avatar of undefined
Last Comment
Avatar of reswobslc

Blurred text
View this solution by signing up for a free trial.
Members can start a 7-Day free trial and enjoy unlimited access to the platform.
See Pricing Options
Start Free Trial
Avatar of giltjr
Flag of United States of America image

What kind of interface/device are you using that requires/uses only 3 wires?  I am assuming you are using software flow control other wise you can't even communicate reliably.

As, reswobslc stated, with only TX and RX you really can't tell because you don't have access to the signals/leads that tell you the status.
Avatar of reswobslc

Actually, 3 wire RS232 is very common.  Just not with modems.

A lot of computer-to-computer links are 3 wire RS232.  Flow control just doesn't make sense much of the time - computers with gigahertz and gigabytes to spare aren't in a position where they are going to boil over receiving 10 KBytes/sec if it can't signal the other guy to slow down.

Modems don't even strictly need flow control either for many applications.  They only started needing it the day they implemented data compression and error correction and offered the ability to use a different bps rate between the modem and computer than on the phone line, when the actual throughput wasn't known in advance.  Even then, many protocols that still use modems simply don't send enough data to ever overflow a buffer.  For example, when a modem is used to validate a credit card transaction, the packets containing the credit card number and dollar amount, as well as the packet containing the approval/decline, are so small the buffer would never overflow, flow control or not.  And 3-wire RS232 controls lots of gadgets inside devices, like LCD displays, keypads, servo controllers, barcode readers, magstripe readers, you name it, and these don't use flow control because they are constrained to processing only tens or hundreds of bytes at a time by their nature and design.
Avatar of mrsisti


you were right i can't do it reliably
Visual Basic.NET
Visual Basic.NET

Visual Basic .NET (VB.NET) is an object-oriented programming language implemented on the .NET framework, but also supported on other platforms such as Mono and Silverlight. Microsoft launched VB.NET as the successor to the Visual Basic language. Though it is similar in syntax to Visual Basic pre-2002, it is not the same technology,

Top Experts
Get a personalized solution from industry experts
Ask the experts
Read over 600 more reviews


IBM logoIntel logoMicrosoft logoUbisoft logoSAP logo
Qualcomm logoCitrix Systems logoWorkday logoErnst & Young logo
High performer badgeUsers love us badge
LinkedIn logoFacebook logoX logoInstagram logoTikTok logoYouTube logo