Low level comm port manipulation

[Justin Ward]

I'm a geophysicist. The program I am writing will monitor the earths' magnetic field via a G856 proton precession magnetometer and warn us of geomagnetic storms.
The Geometrics G856 (www.geometrics.com) can be made to output readings via RS-232 by a "pulse (pull line low) on
"sync" pin S (or connect pin S to pin D). The data will be sent RS-232 (d = ground, T = transmit (from g-856), G = clear to send,)". This is a quote from the manual.

I have wiring and pin diagrams of the RS-232 interface with the G856. So I need RS-232 pin manipulation controls.

Can this kind of low level comm port manipulation be done in VB5? Maybe certain characters sent to the comm port do this???

I doubt that the MSComm control can do this.

Justin.

[Sacred_knight]

Can you give me the wiring and pin diagrams of the RS-232 interface with the G856. I looked up the geometrics website and there no mention of the G-856. I only saw G-858.
I need to know what you stated is actually refering to what signals.

The Geometrics G856 (www.geometrics.com) can be made to output readings via RS-232 by a "pulse (pull line low) on
"sync" pin S (or connect pin S to pin D). The data will be sent RS-232 (d = ground, T = transmit (from g-856), G = clear to send,)".

Anyway here is the actual pin outs for two types of standard serial cables (9 Pin and 25 Pin).

D9---D25

3----2-----TD (Transmit Data)
2----3-----RD (Recieve Data)
5----7-----SG (Signal Ground)
4----20----DTR (Data Terminal Ready)
6----6-----DSR (Data S??? Ready)
1----8-----CD (Carrier Detect)
7----4-----RTS (Request To Send)
8----5-----CTS (Clear To Send)

There are also Null Modem cables. They only use three signals to tranmit data (TD, RD, and SG). The wiring configuration is as follows;

TD
RD
SG
DTR, DSR, and CD are shorted together
RTS and CTS are shorted together

Hope this help.

Reply here or email me at:

[email protected]

[Edited by Sacred_knight on 03-28-2000 at 01:39 PM]

[Justin Ward]

OK - here's the low down from the manual.
We're dealing with RS-232 revision C, and a D9 connector.

The following table lists the functions assigned to each pin of the RS-232 cable from the G-856. Only 3 of 22 standard RS-232C data transmission lines are used in the G-856. The RS-232C interface cable is wired to connect directly to a PC 9-pin serial port.

9-pin RS-232, G-856 Front panel, Function description

2, T, Transmit data from the G856
5, D, Signal ground - zero reference for interface
7, G, Clear to send - When low inhibits G856 output.

Come to think of it this is all irrelevant because I can already accept the output from the device via a MSComm control. There is 1 start bit, 7 data bits, 1 parity bit and 2 stop bits.

The G856 can be set to output data at certain intervals via these lines above. This is fine, I have done this and now need to trigger a reading using the computer.

There is another pin on the front panel of the G856 called the Syncronisation pin (S). I need to connect pin S to pin D in order to trigger a reading. It's low voltage so nothing will get blown up. I can make a cable to connect S to any RS-232 pin I like. Same with G.

So in a nutshell, the problem is:

Can VB be used to switch external devices without using QBasic and relays.
Or alternatively:
Can one serial pin be connected to another using code?
Or alternatively:
Can a serial pin be pulled low using code?

Ideally there would be a function:

Bool SerialPinConnection(Int CommPortID, Int ConnectThisPin, Int 2ThisPin)

The G856 is the older model of the G858.

Justin.

[Jason B]

Hi...
This is an update to my last question.. I was actually trying to read in data from a device using say comm port 1 and uses a protocol called RB8192

before (in dos programming i used to open up the port like this :

where comport$ = "COM1:9600,O,7,2,RB8192"

OPEN comport$ FOR RANDOM AS #1

in qbasic. Need to be able to do this in visual basic 6. Please help as i am stuck!

Jason

[Justin Ward]

Well, that's the last you'll hear from me. Never heard of RB 4095943.

Justin.