Future Technology Devices
International Ltd.
AN232B-09 Using the Modem
Emulation Mode in FTDI's VCP Driver
Copyright © 2005 Future Technology Devices International Ltd.
I
AN232B-09 Modem Emulation Mode
Table of Contents
Part I Introduction
2
Part II Modem Emulation
3
1 Method
................................................................................................................................... 3
2 XOn-XOff ...................................................................................................................................
Software Handshaking
5
3 Enabling Modem
...................................................................................................................................
Emulation Mode
6
Part III Document Revision History
7
Part IV Disclaimer
8
Part V Contact Information
9
0
Index
Copyright © 2005 Future Technology Devices International Ltd.
Introduction
1
2
Introduction
Modem Emulation Mode is a special feature of FTDI's Virtual COM Port (VCP) driver that allows
binary data to be transmitted over a two (or more) wire interface with full handshaking and modem
control signalling, thus allowing PPP connections to be made. Possible applications include mobile
phone data cables and radio links.
Modem Emulation Mode can be setup in the driver INF file (FTDIPORT.INF) or can be enabled in
the registry. Its purpose is to allow modem emulation to be done by the driver when the device
attached is not a standard modem. The reason for this is that many standard applications require
the DCD line to know that they are on the internet (e.g. for Dial Up Networking).
Copyright © 2005 Future Technology Devices International Ltd.
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AN232B-09 Modem Emulation Mode
2
Modem Emulation
2.1
Method
This method can use XOn/XOff or hardware RTS/CTS handshaking. Both the XOn/XOff
characters and the escape character are definable.
The standard ones will be:
XOn - 0x11
XOff - 0x13
EscChar - 0x10
Transmitter
Receiver
Data In
Data Transmitted
Data Received
Data Out
XOn
EscChar + 0x01
EscChar + 0x01
XOn
XOff
EscChar + 0x02
EscChar + 0x02
XOff
EscChar
EscChar + EscChar
EscChar + EscChar
EscChar
0x01
0x01
0x01
0x01
0x02
0x02
0x02
0x02
Flow Control
XOn
XOn
None
Flow Control
XOff
XOff
None
FTDI Driver
Application Hardware
Command In
Data Transmitted
Data Received
Status Out
SetDTR
EscChar + 0x03
EscChar + 0x03
DTR Active
ClrDTR
EscChar + 0x04
EscChar + 0x04
DTR Inactive
0x01
0x01
0x01
0x01
0x02
0x01
0x01
0x01
0x03
0x03
0x03
0x03
0x04
0x04
0x04
0x04
0x05
0x05
0x05
0x05
0x06
0x06
0x06
0x06
0x07
0x07
0x07
0x07
0x08
0x08
0x08
0x08
0x09
0x09
0x09
0x09
0x0A
0x0A
0x0A
0x0A
0x0B
0x0B
0x0B
0x0B
0x0C
0x0C
0x0C
0x0C
0x0D
0x0D
0x0D
0x0D
0x0E
0x0E
0x0E
0x0E
0x0F
0x0F
0x0F
0x0F
Copyright © 2005 Future Technology Devices International Ltd.
Modem Emulation
The following ones are not applicable if RTS/CTS hardware handshaking is used:
FTDI Driver
Application Hardware
Command In
Data Transmitted
Data Received
Status Out
SetRTS
EscChar + 0x05
EscChar + 0x05
RTS Active
ClrRTS
EscChar + 0x06
EscChar + 0x06
RTS Inactive
Application Hardware
FTDI Driver
Command In
Data Transmitted
Data Received
Status Out
SetDSR
EscChar + 0x07
EscChar + 0x07
DSR Active
ClrDSR
EscChar + 0x08
EscChar + 0x08
DSR Inactive
SetDCD
EscChar + 0x09
EscChar + 0x09
DCD Active
ClrDCD
EscChar + 0x0A
EscChar + 0x0A
DCD Inactive
SetRI
EscChar + 0x0B
EscChar + 0x0B
RI Active
ClrRI
EscChar + 0x0C
EscChar + 0x0C
RI Inactive
0x01
0x01
0x01
0x01
0x02
0x02
0x02
0x02
0x03
0x03
0x03
0x03
0x04
0x04
0x04
0x04
0x05
0x05
0x05
0x05
0x06
0x06
0x06
0x06
0x07
0x07
0x07
0x07
0x08
0x08
0x08
0x08
0x09
0x09
0x09
0x09
0x0A
0x0A
0x0A
0x0A
0x0B
0x0B
0x0B
0x0B
0x0C
0x0C
0x0C
0x0C
0x0D
0x0D
0x0D
0x0D
0x0E
0x0E
0x0E
0x0E
The following ones are not applicable if RTS/CTS hardware handshaking is used:
Application Hardware
FTDI Driver
Command In
Data Transmitted
Data Received
Status Out
SetCTS
EscChar + 0x0D
EscChar + 0x0D
CTS Active
ClrCTS
EscChar + 0x0E
EscChar + 0x0E
CTS INactive
Copyright © 2005 Future Technology Devices International Ltd.
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2.2
AN232B-09 Modem Emulation Mode
XOn-XOff Software Handshaking
If the XOn and XOff characters are substituted in this way, then raw binary may be sent without
affecting the flow control. If the transmitter receives the XOff character it should stop transmission
and start it on XOn being received. If the receiver wants to stop transmission it should send the
XOff etc.
Copyright © 2005 Future Technology Devices International Ltd.
Modem Emulation
2.3
6
Enabling Modem Emulation Mode
Modem Emulation mode substitution bits can be enabled by setting the following bits in the VCP
driver INF file FTDIPORT.INF :
HKR,,"EmulationMode",0x00010001,0x0000nnnn {HEX format}
Force XOn/XOff handshaking if any flow control is active - bit 0
For the following substitutions the following convention will be used :
0,0 = off
0,1 = on
1,0 = don't set
1,1 = don't set
Substitute XOn/XOff and Control Char - bit 2,1
Substitute DSR and Control Char - bit 4,3
Substitute RI and Control Char - bit 6,5
Substitute DCD and Control Char - bit 8,7
Substitute CTS and Control Char - bit 10,9
Substitute RTS and Control Char - bit 12,11
Substitute DTR and Control Char - bit 14,13
If the appropriate bit is not set, then the driver will assume the normal method for receiving/setting
the line.
Copyright © 2005 Future Technology Devices International Ltd.
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AN232B-09 Modem Emulation Mode
Document Revision History
Version
Release Date
Comments
1.0
March 2004
Initial release
2.0
May 2005
"Data Out" or "Status Out" column added to each table.
Copyright © 2005 Future Technology Devices International Ltd.
Disclaimer
4
8
Disclaimer
Copyright © 2005 Future Technology Devices International Ltd.
Neither the whole nor any part of the information contained in, or the product described in this
manual, may be adapted or reproduced in any material or electronic form without the prior written
consent of the copyright holder.
This product and its documentation are supplied on an as-is basis and no warranty as to their
suitability for any particular purpose is either made or implied.
Future Technology Devices International Ltd. will not accept any claim for damages howsoever
arising as a result of use or failure of this product. Your statutory rights are not affected.
This product or any variant of it is not intended for use in any medical appliance, device or system
in which the failure of the product might reasonably be expected to result in personal injury.
This document provides preliminary information that may be subject to change without notice.
Copyright © 2005 Future Technology Devices International Ltd.
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AN232B-09 Modem Emulation Mode
Contact Information
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Copyright © 2005 Future Technology Devices International Ltd.