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Com Ports - Technical Information
Handshaking
An integral part of managing the receive and transmit buffers is ensuring that the back-and-forth transmission of data is successful — that the speed at which the data is being received does not overflow the buffer limits, for example.
Handshaking refers to the internal communications protocol by which data is transferred from the hardware port to the receive buffer. When a character of data arrives at the serial port, the communications device has to move it into the receive buffer so that your program can read it. A handshaking protocol ensures that data is not lost due to a buffer overrun, where data arrives at the port too quickly for the communications device to move the data into the receive buffer.
You set the Handshaking property to specify the handshaking protocol to be used by your application. By default, this value is set to none (comNone). You can, however, specify one of the other following protocols:
| Setting | Value | Description |
| comNone | 0 | No handshaking (Default). |
| comXOnXOff | 1 | XOn/XOff handshaking. |
| comRTS | 2 | RTS/CTS (Request To Send/Clear To Send) handshaking. |
| comRTSXOnXOff | 3 | Both Request To Send and XOn/XOff handshaking. |
The protocol that you choose depends upon the device to which you’re connecting.
Setting this value to comRTSXOnXOff supports both of the protocols.
In many cases, the communications protocol itself handles handshaking. Therefore, setting this property to something other than comNone may result in conflicts.
Note If you do set this value to either comRTS or comRTSXOnXOff, you need to set the RTSEnabled property to True. Otherwise, you will be able to connect and send, but not receive, data.
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Hi U
Can U show me some page ,apllicate this code by VB . U can send my mail kychinh2002@yahoo.com
thanks,i need it so much
Hi U
Can U show me some page ,apllicate this code by VB
thanks,i need it so much
i am using mscomm with visual basic. i want to read/write data on serial port rs232. what code will i have to write and what properties i will have to change in mscomm. please help me as soon as possible.
Do you know what command to issue so that when i call up the receiver's HP, i can get to know whether the receiver phone is ringing? and count the number of times the phone ring?? get i get those reponse? cause i am trying to do a miss call.
In order to do that i need to know whether the phone rings .. if so i will let the phone ring for 3 times ... then hang up
..
Another question is :
comEvRing "6"
Ring detected. Some UARTs (universal asynchronous receiver-transmitters) may not support this event.
i understand that the above means that ring is detected. when the CommEvent is "6". However, what does it mean some UARTs may not support it ...
Can any expert show me what that means? i dont seem to understand it.
and my current modem is :
3COM US ROBOTICS 56K FaxModem Model (455630-01)
does my modem support that?
do your problem has solved?
I meet the same problem now, visual basic text doesn't give any response to binary input.
I really need your solution, if you already have it
thanks
Modem CODES AT Attention Code. Must appear at start of all commands except A/ and +++.
A Answer Command. Answer incoming call.
A/ Repeat Last Command.
Bn Bell Compatibility
B,B0 Variable connection rate ITU-T (CCITT) Compatibility.
B1 Variable connection rate Bell Compatibility.
B2 Auto-mode V.22/Bell 212A protocols.
B4 300 bps Bell 103 protocol.
B5 1200 bps V.22/Bell 212A protocols.
B6 2400 bps V.22/bis protocol.
B7 4800 bps V.32 protocol.
B8 9600 bps V.32 protocol.
B9 14,400 bps V.32 bis protocol.
Ds Dialing Command
DP Dialing Command. Pulse Dialing.
DR Dialing Command. Reverse.
DS Dialing Command. Dial one of the srored numbers.
DT Dialing Command. Tone Dialing.
D@ Dialing Command. Wait for 5 seconds quiet.
D, Dialing Command. Pause.
D; Dialing Command. Resume command mode after dialing.
D! Dialing Command. Hook Flash.
E Echo Command
E,E0 Echo Off.
E1 Echo On.
Hn Switch-Hook Control.
H,H0 On Hook (hang up phone).
H1 Off Hook (pick up phone).
In Request Product Code and Checksum.
I,I0 Return Product Code.
I1 ROM checksum, product ID, ROM version number.
I2 Compute ROM checksum.
I3 Error Correctio Code.
I4 Product ID, ROM version number, modem chip type, fax operatnig mode.
Ln Speaker Volume
L,L0,L1 Speaker Volume. Low Volume.
L2 Speaker Volume. Medium Volume.
L3 Speaker Volume. High Volume.
Mn Monitor on/off
M,M0 Speaker off.
M1 Speaker on until online.
M2 Speaker always on.
M3 Speaker on until online and off while dialing.
On Return to online mode.
O,O0 Return to online mode.
O1 Return to online mode and start retrain sequence.
O2 Fall forward. Return to online mode.
O3 Fall back. Return to online mode.
P Pulse dialing.
Qn Quiet Command
Q,Q0 Display result codes.
Q1 Don't display result codes.
Q2 Display result codes when originating a call.
Q3 Return numeric results 32 and 30 for CONNECT 9600 and CONNECT 4800.
Q4 Return numeric results 12 and 11 for CONNECT 9600 and CONNECT 4800.
Sr Direct Register Command
Sn Select register n as default register.
Sn? Read and display value in register n.
Sn?^ Read and display value in register n in HEX.
Sn=N Set register n to value N.
Sn=N^ Set register n to value N in HEX
Vn Verbal/Numeric Result Codes.
U Update System password.
V,V0 Numeric Result Codes.
V1 Verbal Result Codes.
Xn Enable Extended Result Code
X,X0 No wait for dial tone. No busy. CONNECT 0-4 returned.
X1 No wait for dial tone. No busy. CONNECT 0-5 and 9-20 returned.
X2 Wait for dial tone. No busy. CONNECT 0-6 and 9-20 returned.
X3 No wait for dial tone. Busy recognized. CONNECT 0-5,7 and 9-20 returned.
X4 Wait for dial tone. Busy recognized. CONNECT 0-7 and 9-20 returned.
Y Long Space Disconnect
Z Reset Command
&V Display al stored profiles.
&Zn=s Store telephone number.
+++ Escape Code. Switch from data mode to command mode.
thanks to Oliver Lawrence lawrence@cdnet.cod.edu <lawrence@cdnet.cod.edu>
Good Day,
I'm using VB6 MSComm with "2400,n,7,1" (settings) to dial up using ArtNet modem. I couldn't get any dial tone with the mentioned setting. However, when i change to "2400,n,8,1" it will be able to dial up ? When i use hyperterminal with "2400,n,7,1" to dial up, no problem at all. Any idea what's wrong ? Thanks in advance.
I really loved this article, nice one!
Here is a complete list of all the AT commands I could get..
-----------------------------------------------------------------------------------------------------------------------------------
Table 1. Basic Data Modem AT Commands
-----------------------------------------------------------------------------------------------------------------------------------
A/ Repeat the last AT command string issued.
An “AT” prefix is not used. Do not terminate this command
with <ENTER>.
A Answer.
Go off-hook and enter the answer mode. After 3 seconds the
modem will initiate an answer tone.
Bn ITU-T or Bell® (Default=1)
B0 Use ITU-T V.22 at 1200 bps, and ITU-T V.21at 300 bps
B1 Use Bell® 212A at 1200 bps, Bell® 1035 at 300 bps.
B2 Use ITU-T V.23 only. The originating modem transits at 75
bps (and receives at 1200 bps); the answering modem receives
at 75 bps (and transmits at 1200 bps)
B3 Selects ITU-T V.23 only. The originating modem transmits at
1200 bps (and receives at 75 bps); the answering modem
receives at 1200 bps (and transmits at 75 bps)
Cn Carrier control option (Default=1)
C0 Transmit carrier always off
C1 Normal transit carrier
D Dial command
En Command Echo (Default=l)
E0 Disables command echo from the modem.
E1 Enables command echo from the modem.
Fn Online echo (Default=1)
F0 Enables online echo
F1 Disables online echo
Hn Hook Switch Control (Default=0)
H0 Hangs up the telephone line
H1 Picks up the telephone line
In Identification/checksum option (Default=0)
I0 Reports product code
I1 Reports modem chip firmware version
I2 Verifies ROM checksum
I3 Reports device set name
I4 Reserved
I5 Reserved for modem chip hardware configuration
I6 Country code
I7 Version of board manufacturer firmware
I8 Features of modem firmware
I10 Modem board configuration - bit set by board manufacturer
I11 Modem board configuration - bits set by board manufacturer
I14 SAFE device
I20 Cirrus Logic silicon version
I21 Cirrus Logic firmware version
I22 Cirrus Logic manufacturer name
I23 Cirrus Logic product model
Ln Speaker Volume control (Default=2)
L0,1 Low volume.
L2 Medium speaker volume
L3 High speaker volume
Mn Speaker On/Off (Default=1)
M0 Speaker off.
M1 Speaker on until modem detects the carrier signal.
M2 Speaker is always on when modem is off-hook.
M3 Speaker off during dialing, on until modem carrier present
Nn Select data rate handshake (Default=1)
N0 Handshake only at DTE-to-modem data rate
N1 Begins handshake at DTE-to-modem data rate and falls to
highest compatible rate
On Go Online (Default=0)
O0 Returns modem to data mode
O1 Retrains equalizer and then returns to data mode
P Pulse Dial
Qn Result Codes (Default = 0)
Q0 Enables display of result codes
Q1 Disables display of result codes
Sn Select an S-register
Sn=x Write to an S-Register
Sn? Read from an S-Register
T Tone Dial
Vn Result Codes Format (Default=1)
V0 Enable short-form result codes. (Numeric)
V1 Enable long-form result code. (Text or Verbose)
Wn Response code data rate (Default=0)
W0 Reports DTE speed response codes
W1 Reports DTE speed response codes
W2 Reports DCE speed response codes
W3 Reports DTE speed response codes and information on error
correction and data compression
Xn Result Code type (Default=4)
X0 Enables result codes 0-4; disables detection of busy and dial
tone
X1 Enables result codes 0-5, 10, and above; disables busy and dial
tone detection
X2 Enables result codes 0-6 and 10 and above; disables busy
detection and enables dial tone detection
X3 Enables result codes 0-5, 7, and 10 and above; enables busy
detection and disables dial tone detection
X4 Enables result codes 0-7 and 10 and above; enables busy and
dial tone detection
Yn Long Space Disconnect (Default=0)
Y0 Disable Long Space Disconnect
Y1 Enable Long Space Disconnect
Zn Recall stored profile (Default=0)
Z0 Resets modem and recalls user profile 0
Z1 Resets modem and recalls user profile 1
&Cn DCD (data carrier detect) option (Default=1)
&C0 Ignores remote modem status; DCD always on
&C1 DCD set according to remote modem status
&Dn DTR Control, Data Terminal Ready (Default=2)
&D0 In async mode, modem ignores DTR
&D1 Modem switches to command mode when DTR switches on
&D2 When DTR switches off, the modem goes on-hook and
disables auto-answer mode; when DTR switches on, autoanswer
is enabled
&D3 Turning off DTR re-initializes the modem and resets values
except UART registers
&F Load factory defaults
&Gn Guard tone option (1200 bps and 2400
Even if I use Binarymode but my data was received is not format that my equipment was send. (My data can't converted by Cint() or Cbyte(), only Val() can converted it but result is zero).
How I can receive binary data by MSCOMM?
http://www.angelfire.com/linux/jsanchez/NullmodemCables.htm
SEND ME AN EMAIL FOR GIVE MORE BEST TECHNICAL HELP.
GOOD DAY!!! AND HARE KRISHNA
you need know how make a null modem cable?
I want to communicate throught the com1 port using a Null modem cable. I need help in this regard.
i am using MSComm with Visual Basic . it does not read or write anything on the port. i dont have modem in my pc. i only want to read data from serail port rs232. i am using a time and attandance recorder which sends data on com1 and shows it on its software but when i read it with MSCOmm it shows nothing. Mscomm1.intBufferSize is o . please help me soon.
I want to design 2 programs Client /server which comunicate thru phone line, using MScomm Control.
But i don't know how to make Mscomm waiting for a call like We do with Winsocket.
could you kindly help me?
This thread is for discussions of Com Ports - Technical Information.