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CP210 X V IRTUAL COM P ORT I NTERFACE
1. Introduction
This document describes the CP210x Virtual COM Port interface between the host and CP210x device for the
purposes of creating custom drivers that interface with the CP210x. For more information on how to customize the
CP210x hardware, see “AN144: CP210x/CP211x Device Customization Guide” on the Silicon Labs Application
Notes webpage:
https://www.silabs.com/products/mcu/Pages/ApplicationNotes.aspx
1.1. Related Documents
Universal Serial Bus Specification: version 2.0 (also referred to as the USB Specification). This specification is
available at http://www.usb.org.
Universal Serial Bus Class Definitions for Communication Devices: version 1.1 (also referred to as the CDC
Specification, where “CDC” stands for “Communication Device Class”. This specification is available at http://
www.usb.org.
ANSI/TIA-602: Serial Asynchronous Automatic Dialing and Control - available at http://www.eia.org.
1.2. Terms
end device: refers to the hardware connected to the CP210x UART pins.
host: refers to the PC driver and host controller.
2. Interface Architecture
The CP210x device implements one or more communications interfaces implemented using the Bulk protocol.
These USB Bulk pipes transport data only and any status information must be obtained from the control pipe.
To configure and control the port, the host sends requests to the device via the control pipe. The host uses these
requests to perform such functions as setting the baud rate, setting handshaking modes, and configuring special
characters.
To send data from the host to the port, the host queues BULK-OUT packets to the endpoint of the interface
associated with the port. The data from these packets will be loaded into the interface’s data buffers and passed on
to the external device.
To move data from the port to the host, the host issues IN requests to the port’s data IN endpoint.
Rev. 0.1 12/10
Copyright © 2010 by Silicon Laboratories
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3. Flow Control
The Virtual COM Port protocol is designed to allow ports to perform the same handshaking that is performed by
PCs when running Windows with a real serial port. To do this, the device is required to follow detailed rules for flow
control.
The Virtual COM Port protocol provides full-duplex data streams. The transmit stream is used for data from the
host to the serial port; the receive stream is used for data from the serial port to the host. Each stream has
provisions for flow control.

Transmit flow control allows the end device to ask the port to stop transmitting data. The CP210x will continue
to accept OUT data from the host until its internal buffers are full, and then will NACK further OUT packets to the
transmit endpoint. When the end device has accepted enough data from the CP210x buffers, the CP210x will
accept more OUT packets from the host.
 Receive flow control allows the port to ask the end device to stop transmitting data to the host. The CP210x
device holds the data received from the end device in buffers until the host asks for it. If the host does not ask
for data in a timely fashion (usually because the application is busy), the CP210x’s buffers may start to fill up,
and the CP210x uses receive flow control to ask the end device to stop sending data. When the host catches
up and empties the CP210x’s buffers, the CP210x then uses receive flow control to ask the end device to
resume sending data.
All flow-control handling is performed in the CP210x device. This is done for two reasons:

To reduce overhead at the host.
 To eliminate latency for responding to flow-control events.
The host’s only involvement with flow control is to set the device into the desired flow control mode.
3.1. XON/XOFF Flow Control
Two characters are defined by the “set special characters” mechanism (SET_CHARS): XON (normally 0x11,
CTRL/Q), and XOFF (normally 0x13, CTRL/S). The same values are used for XON and XOFF for both transmit
and receive flow control. XON and XOFF may be set to the same character, but usually are different.
The CP210x device follows “OS/2 rules:” if transmit flow control says “don’t transmit”, the port prevents any
characters from being transmitted, including the flow control characters. The device normally stops transmitting
whenever it sends XOFF for receive flow control. The port resumes transmitting only when it sends XON to allow
the remote device to send data. This prevents a potential buffer overflow because the flow control characters
cannot be transmitted while XOFF is in effect.
3.2. Flow Control Rules







2
The CP210x uses a bit pattern similar to the ulHoldReasons mask from the Serial Status response (see Table 8)
to control transmission. If any of the hold reasons are set, the CP210x will not send (except that certain
characters, such as XON for receive flow control, can always be sent).
If the CP210x sends an XOFF special character in order to stop reception, the device will transmitting until the
device decides to send XON. While transmission is halted, the CP210x will set bit 4 in ulHoldReasons (see
Table 8).
If the CP210x receives an XOFF special character and is configured to XON/XOFF flow control mode, then the
CP210x will stop transmitting characters. While stopped, the CP210x sets bit 3 in ulHoldReasons. When an
XON is received, the CP210x clears bit 3 in ulHoldReasons and resumes transmission if ulHoldReasons [5..0]
is now zero.
If the CP210x is instructed to send a BREAK, it will stop sending normal characters while BREAK is asserted
and set bit 5 of ulHoldReasons.
If the CP210x is waiting for any of the modem control signals CTS, DSR or DCD, the CP210x sets the
appropriate bits in ulHoldReasons when the corresponding signal is causing a delay; the device will clear those
bits when the hold condition is removed, either because the flow-control programming was changed, or
because the signal changed state externally.
Immediate characters are not blocked by software flow control (either due to XOFF sent or due to XOFF
received). However, they are held off by BREAK, CTS handshaking, DSR handshaking or DCD handshaking (if
enabled and holding off traffic).
After sending an XOFF, the CP210x sends XON to start receiving data only if output is not being held, or
otherwise if either a sent XOFF or a received XOFF is the only reason that output is being held.
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4. CP210x Hardware Descriptors
The CP210x device descriptor contains zero in the bDeviceClass, bDeviceSubClass, and bDeviceProtocol fields.
All other fields are set as defined in Section 9.6.1 "Device" of the USB Specification.
Table 1. CP210x Default Device Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
0x12
Size of the descriptor in bytes.
1
bDescriptorType
1
0x01
Device descriptor type code.
2
bcdUSB
2
0x0110 or 0x0200
Claimed version compliance, where the
LSB is the low order and the MSB is the
high order (0x0100 is version 1.0).
4
bDeviceClass
1
0x00
Indicates that this device is of no particular device class.
5
bDeviceSubClass
1
0x00
Inidicates that there’s no particular subclass.
6
bDeviceProtocol
1
0x00
No device-specific protocol.
7
bMaxPacketSize
1
0x40
Indicates the maximum packet size for
Endpoint0.
8
idVendor
2
0x10C4
10
idProduct
2
12
bcdDevice
2
0x0100
14
iManufacturer
1
0x01
Manufacturer string descriptor index.
15
iProduct
1
0x02
Product string descriptor index.
16
iSerialNumber
1
0x03 or 0x05
17
bNumConfigurations
1
0x01
Manufacturer’s Vendor ID.
0xEA60 or 0xEA70 Manufacturer’s Product ID.
Rev. 0.1
Product version in BCD.
Serial string descriptor index.
Number of possible configurations.
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Table 2. CP210x Default Configuration Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
0x09
Size of the descriptor in bytes.
1
bDescriptorType
1
0x02
Configuration descriptor type code.
2
wTotalLength
2
0x0020 or 0x0037
4
bNumInterfaces
1
0x01 or 0x02
Number of interfaces in this configuration (CP2105 has two interfaces).
5
bConfigurationValue
1
0x01
Indicates the value to be used in a Set
Configuration packet to activate this
configuration.
6
iConfiguration
1
0x00
Index of the string descriptor describing
this configuration.
7
bmAttributes
1
0x80
Indicates the characteristics of the
device when this configuration is
selected:
Total length of data returned for configuration 0 (stored in little-endian order).
bit 7 set: Device is bus powered.
bit 6 set: Device is self powered.
bit 5-0: reserved.
8
4
MaxPower
1
0x32
Rev. 0.1
Maximum power consumption in 2mA
units. For self-powered devices, this
field is zero.
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Table 3. CP210x Default Interface Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
0x09
Size of the descriptor in bytes.
1
bDescriptorType
1
0x04
Interface descriptor type code.
2
bInterfaceNumber
1
0x00 or 0x01
3
bAlternateSetting
1
0x00
Indicates the alternate setting which
enables the interface to operate as
described.
4
bNumEndpoints
1
0x02
This interface has 2 Endpoints.
5
bInterfaceClass
1
0xFF
Indicates that this is a vendor-specific
interface.
6
bInterfaceSubClass
1
0x00
No particular subclass.
7
bInterfaceProtocol
1
0x00
The interface uses no specific protocol.
8
iInterface
1
The interface described by this descriptor (CP2105 devices have two interfaces).
0x02, 0x03, or 0x04 Index of the string descriptor describing
this interface.
Table 4. CP210x Default IN Endpoint Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
0x07
Size of the descriptor in bytes.
1
bDescriptorType
1
0x05
Endpoint descriptor type code.
2
bEndpointAddress
1
0x81 or 0x82
3
bmAttributes
1
0x02
4
wMaxPacketSize
2
0x0040 or 0x0020
5
bInterval
1
0x00
Rev. 0.1
IN Endpoint (either Endpoint 1 or Endpoint 2).
Bulk Endpoint.
The maximum packet size is 64 or 32
bytes.
Not used for Bulk Endpoints.
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Table 5. CP210x Default OUT Endpoint Descriptor
6
Offset
Field
Size
Value
Description
0
bLength
1
0x07
Size of the descriptor in bytes.
1
bDescriptorType
1
0x05
Endpoint descriptor type code.
2
bEndpointAddress
1
0x01 or 0x02
3
bmAttributes
1
0x02
4
wMaxPacketSize
2
0x0040 or 0x0020
5
bInterval
1
0x00
Rev. 0.1
OUT Endpoint (either Endpoint 1 or
Endpoint 2).
Bulk Endpoint.
The maximum packet size is 64 or 32
bytes.
Not used for Bulk Endpoints.
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5. CP210x Control Commands
The CP210x commands in Table 6 follow the standard USB Setup packet structure and are defined in addition to
the messages defined as part of Chapter 9 of the USB Specification. The interface number can be obtained from
the CP210x descriptors upon enumeration and driver load. This section discusses each of these commands.
Table 6. Interface Commands
Name
Code
Description
IFC_ENABLE
0x00
Enable or disable the interface.
8
SET_BAUDDIV
0x01
Set the baud rate divisor.
8
GET_BAUDDIV
0x02
Get the baud rate divisor.
8
SET_LINE_CTL
0x03
Set the line control.
9
GET_LINE_CTL
0x04
Get the line control.
10
SET_BREAK
0x05
Set a BREAK.
14
IMM_CHAR
0x06
Send character out of order.
14
SET_MHS
0x07
Set modem handshaking.
10
GET_MDMSTS
0x08
Get modem status.
11
SET_XON
0x09
Emulate XON.
11
SET_XOFF
0x0A
Emulate XOFF.
12
SET_EVENTMASK
0x0B
Set the event mask.
12
GET_EVENTMASK
0x0C
Get the event mask.
13
GET_EVENTSTATE
0x16
Get the event state.
13
SET_CHAR
0x0D
Set special character individually.
14
GET_CHARS
0x0E
Get special characters.
15
GET_PROPS
0x0F
Get properties.
15
GET_COMM_STATUS
0x10
Get the serial status.
14
RESET
0x11
Reset.
8
PURGE
0x12
Purge.
15
SET_FLOW
0x13
Set flow control.
11
GET_FLOW
0x14
Get flow control.
11
EMBED_EVENTS
0x15
Control embedding of events in the data stream.
16
GET_BAUDRATE
0x1D
Get the baud rate.
9
SET_BAUDRATE
0x1E
Set the baud rate.
8
SET_CHARS
0x19
Set special characters.
15
VENDOR_SPECIFIC
0xFF
Vendor specific command.
17
Rev. 0.1
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5.1. IFC_ENABLE (0x00)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
IFC_ENABLE
Boolean
interface
0
None
This command enables or disables the specified CP210x interface. If wValue is 0x0001, the interface is enabled
and serial data can be transmitted. If wValue is zero, the interface is disabled.
Host drivers should enable the interface before sending any of the other commands specified by this document.
For maximum compatibility with Windows, the CP210x will not change its baud rate or line control parameters on
enable or disable. However, the CP210x may lower DTR.
5.2. RESET (0x11)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
RESET
0
interface
0
None
This command is in place for compatibility reasons. The CP210x device will ignore this command.
5.3. SET_BAUDDIV (0x01)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_BAUDDIV
baud rate
divisor
interface
0
None
This command sets the baud rate for the specified interface according to wValue. The value is determined by
dividing the desired baud rate into 3.6864 MHz.
5.4. GET_BAUDDIV (0x02)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_BAUDDIV
0
interface
2
baud rate divisor
This command gets the baud rate for the specified interface. The value is determined by multiplying the baud rate
divisor returned by 3.6864 MHz.
5.5. SET_BAUDRATE (0x1E)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_BAUDRATE
0
interface
4
baud rate
This command sets the baud rate for the specified interface, according to a 4-byte value specified in the Data
phase of the control request.
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5.6. GET_BAUDRATE (0x1D)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_BAUDRATE
0
interface
4
baud rate
This command gets the baud rate for the CP210x interface.
5.7. SET_LINE_CTL (0x03)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_LINE_CTL
line control
interface
0
None
This command adjusts the line control settings for the selected CP210x interface, according to the value of wValue.
The settings will only take effect if the selection is valid for the interface (see the specific CP210x data sheet for
more details). If an invalid setting is selected, the CP210x will issue a USB procedural stall. The settings are as
follows:
bits 3-0: Stop bits:
0 = 1 stop bit
1 = 1.5 stop bits
2 = 2 stop bits
other values reserved.
bits 7-4: Parity setting:
0 = none.
1 = odd.
2 = even.
3 = mark.
4 = space.
other values reserved.
bits 15-8: Word length, legal values are 5, 6, 7 and 8.
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5.8. GET_LINE_CTL (0x04)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_LINE_CTL
0
interface
2
line control
This command gets the line control settings for the selected CP210x interface. The settings are as follows:
bits 3-0: Stop bits:
0 = 1 stop bit.
1 = 1.5 stop bits.
2 = 2 stop bits.
other values reserved.
bits 7-4: Parity setting:
0 = none.
1 = odd.
2 = even.
3 = mark.
4 = space.
other values reserved.
bits 15-8: Word length, legal values are 5, 6, 7 and 8.
5.9. SET_MHS (0x07)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_MHS
bit mask
interface
0
None
This command sets the modem handshaking states for the selected CP210x interface according to the value of
wValue. DTR and RTS values can be set only if the current handshaking state of the interface allows direct control
of the modem control lines.
bit 0: DTR state.
bit 1: RTS state.
bits 2–7: reserved.
bit 8: DTR mask, if clear, DTR will not be changed.
bit 9: RTS mask, if clear, RTS will not be changed.
bits 10–15: reserved.
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5.10. GET_MDMSTS (0x08)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_MDMSTS
0
interface
1
modem status
This command returns the current states of the RS-232 modem control lines for the specified CP210x interface.
The modem control line status byte is defined as follows:
bit 0: DTR state (as set by host or by handshaking logic in CP210x).
bit 1: RTS state (as set by host or by handshaking logic in CP210x).
bits 2–3: reserved.
bit 4: CTS state (as set by end device).
bit 5: DSR state (as set by end device).
bit 6: RI state (as set by end device).
bit 7: DCD state (as set by end device).
5.11. SET_FLOW (0x13)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_FLOW
0
interface
0x0010
See Table 9
This command sets the flow control state of the specified CP210x interface.
5.12. GET_FLOW (0x14)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_FLOW
0
interface
0x0010
See Table 9
This command gets the flow control state of the specified CP210x interface.
5.13. SET_XON (0x09)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_XON
0
interface
0
None
Emulate the receipt of XON (transmit flow control). If the CP210x interface was in XOFF state and if hardware
handshaking permits, the interface will resume transmitting data to the external device.
If the CP210x interface is not waiting for XON, this command has no effect.
Rev. 0.1
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5.14. SET_XOFF (0x0A)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_XOFF
0
interface
0
None
Emulate the receipt of XOFF (transmit flow control) from the end device. The CP210x interface will stop sending
characters to the end device as soon as possible and will not resume until an XON is received from the end device,
or else SET_XON is received from the host. The interface may continue to accept BULK OUT packets if there is
enough buffer memory available inside the device.
If the CP210x interface is already stopped, this command has no effect.
5.15. SET_EVENTMASK (0x0B)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_EVENTMASK
wait mask
interface
0
None
wValue represents the wait mask as follows:
bit 0: RI trailing edge occurred.
bit 1: unused.
bit 2: The receive buffer is 80% full.
bits 3–7: unused.
bit 8: Character received.
bit 9: Special character received.
bit 10: The transmit queue is empty.
bit 11: CTS state changed.
bit 12: DSR state changed.
bit 13: DCD state changed.
bit 14: Line break received.
bits 15: A line-status error occurred.
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5.16. GET_EVENTMASK (0x0C)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_EVENTMASK
0
interface
2
wait mask
Data represents the wait mask as follows:
bit 0: RI trailing edge occurred.
bit 1: unused.
bit 2: The receive buffer is 80% full.
bits 3–7: unused.
bit 8: Character received.
bit 9: Special character received.
bit 10: The transmit queue is empty.
bit 11: CTS state changed.
bit 12: DSR state changed.
bit 13: DCD state changed.
bit 14: Line break received.
bits 15: A line-status error occurred.
5.17. GET_EVENTSTATE (0x16)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_EVENTSTATE
0
interface
2
event state
Data represents the event state as follows:
bit 0: RI trailing edge occurred.
bit 1: unused.
bit 2: The receive buffer is 80% full.
bits 3–7: unused.
bit 8: Character received.
bit 9: Special character received.
bit 10: The transmit queue is empty.
bit 11: CTS state changed.
bit 12: DSR state changed.
bit 13: DCD state changed.
bit 14: Line break received.
bits 15: A line-status error occurred.
Rev. 0.1
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5.18. SET_BREAK (0x05)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_BREAK
break state
interface
0
None
If wValue is 0x0001, then a BREAK is transmitted. If wValue is 0x000, then BREAK is reset. This is not necessarily
synchronized with queued transmit data. This command is not supported on the second CP2105 interface.
5.19. GET_COMM_STATUS (0x10)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_COMM_STATUS
0
interface
0x0013
See Table 8
This command will return the serial status of the CP210x interface specified by wIndex. The returned Serial Status
structure has information on the amount of data in the CP210x’s transmit and receive queues and other
transmission information.
5.20. IMM_CHAR (0x06)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
IMM_CHAR
char
interface
0
None
The character specified by wValue (which must be in the range 0x00-0xFF) is queued to be transmitted as soon as
possible (bypassing any characters waiting in the queue).
The CP210x will return an error if the value of wValue is out of range.
Because the default pipe is a shared resource, the CP210x will not delay completion of this request. If IMM_CHAR
is received and the device cannot buffer the character immediately, the CP210x will return an error indication.
5.21. SET_CHAR (0x0D)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_CHAR
special char
and index
value
interface
0
None
The individual special character values are set using wValue as follows:
bits 0–7: Index of the character to set:
0 = EofChar
1 = ErrorChar
2 = BreakChar
3 = EventChar
4 = XonChar
5 = XoffChar
bit 8–15: Character value to set for the specified index.
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5.22. SET_CHARS (0x19)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
SET_CHARS
0
interface
0x0006
See Table 12
The special character values are set using the six-byte array passed as Data. It is an error for the host to send
anything other than six bytes, and the CP210x will return an error if this occurs.
5.23. GET_CHARS (0x0E)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_CHARS
0
interface
0x0006
See Table 12
The special character values are returned using the six-byte array passed as Data.
5.24. GET_PROPS (0x0F)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
GET_PROPS
0
interface
0x0100
See Table 7
This command causes the interface to respond with a communication properties response that describes the
capabilities of this interface. The details of this response are shown in Table 7.
5.25. PURGE (0x12)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
PURGE
mask; see
below
interface
0
None
This command causes the CP210x to purge the selected transmit or receive queues, based on the value of the
mask. The bit meanings are as follows:
bit 0: Clear the transmit queue.
bit 1: Clear the receive queue.
bit 2: Clear the transmit queue.
bit 3: Clear the receive queue.
Rev. 0.1
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5.26. EMBED_EVENTS (0x15)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
EMBED_EVENTS
0 or escape
character
interface
0
None
This command selects or deselects event insertion mode, depending on the value of wValue. If wValue is zero,
then the CP210x-to-host data stream consists only of data from the serial port. If wValue is non-zero, then events
are multiplexed with data. Events are marked by a special character selected by wValue (which must be in the
range 0x01-0xFF), followed by one or more bytes of qualifying code. The CP210x will check wValue and return an
error indication if wValue is out of range.
Event insertion mode is disabled by USB device reset or interface disable (IFC_ENABLE with wValue == 0x0000).
The CP210x will mark events by interleaving special characters in the data stream transmitted to the PC. Events
are marked as follows (<ESCCHAR> is the value selected by wValue):
<ESCCHAR> <0x00>: Indicates that the <ESCCHAR> itself appeared in the input stream.
<ESCCHAR> <0x01> <lsrval> <dataval>: Indicates that a line status register change occurred when a
data byte was waiting to be received. <lsrval> is the new line status register value; <dataval> is the next
data character.
<ESCCHAR> <0x02> <lsrval>: Indicates that a line status register change occurred when no data byte
was waiting to be received. <lsrval> is the new line status register value.
<ESCCHAR> <0x03> <msrval>: Indicates that a modem status register change has occurred. <msrval>
is the new value.
The Line Status Register value is encoded as follows:
bit 0: Data ready, Only set when the port is encoding an event with both <lsrval> and <dataval> bytes (that
is, if the sequence is <ESCCHAR> <0x01> <lsrval> <dataval>).
bit 1: Hardware Overrun, A receiver hardware overrun occurred.
bit 2: Parity Error, A parity error occurred.
bit 3: Framing error, A framing error occurred.
bit 4: Break, A break was detected.
bits 5–7: reserved (always 000).
The Modem Status Register value is encoded as follows:
bit 0: Delta CTS, Set if there has been a change in CTS.
bit 1: Delta DSR, Set if there has been a change in DSR.
bit 2: Trailing edge RI, Set if the falling edge of RI has occurred.
bit 3: Delta DCD, Set if there has been a change in DCD.
bit 4: CTS, Current state of CTS.
bit 5: DSR, Current state of DSR.
bit 6: RI, Current state of RI.
bit 7: DCD, Current state of DCD.
16
Rev. 0.1
AN571
5.27. VENDOR_SPECIFIC (0xFF)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
See below
VENDOR_SPECIFIC
See below
See below
See below
See below
This command is used for any vendor specific commands. These are as follows:
5.27.1. WRITE_LATCH (CP2103/4)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
VENDOR_SPECIFIC
0x37E1
write latch
value
0
None
The write latch value that is supplied in wIndex is represented as follows:
bits 0–7: Mask of the latch state (in bits 8-15) to write, where bit 0 is GPIO0, bit 1 is GPIO1, etc. up tp
GPIOn where n is the total number of GPIO pins the interface supports.
bits 8–15: Latch state to write, where bit 8 is GPIO0, bit 9 is GPIO1, etc. up to GPIOn where n is the total
number of GPIO pins the interface supports.
5.27.2. WRITE_LATCH (CP2105)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
01000001b
VENDOR_SPECIFIC
0x37E1
interface
2
write latch value
The write latch value that is supplied in the Data phase is represented as follows:
bits 0–7: Mask of the latch state (in bits 8-15) to write, where bit 0 is GPIO0, bit 1 is GPIO1, etc. up tp
GPIOn where n is the total number of GPIO pins the interface supports.
bits 8–15: Latch state to write, where bit 8 is GPIO0, bit 9 is GPIO1, etc. up to GPIOn where n is the total
number of GPIO pins the interface supports.
5.27.3. READ_LATCH (CP2103/4)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
VENDOR_SPECIFIC
0x00C2
0
1
read latch value
The read latch value that is returned is represented as follows:
bits 0–7: Current latch state, where bit 0 is GPIO0, bit 1 is GPIO1, etc. up to GPIOn where n is the total
number of GPIO pins the interface supports.
5.27.4. READ_LATCH (CP2105)
bmRequestType
bRequest
wValue
wIndex
wLength
Data
11000001b
VENDOR_SPECIFIC
0x00C2
interface
1
read latch value
The read latch value that is returned is represented as follows:
bits 0–7: Current latch state, where bit 0 is GPIO0, bit 1 is GPIO1, etc. up to GPIOn where n is the total
number of GPIO pins the interface supports.
Rev. 0.1
17
AN571
6. Control Formats
This section describes the additional data structures that are transmitted or received in conjunction with the
commands discussed in "5. CP210x Control Commands" on page 7.
Table 7. Communication Properties Response
Offset
Field
Size
Value
0
wLength
2
Number: 0x????
2
bcdVersion
2
BCD: 0x0100
Version of response, in BCD: 0x0100 is
Version 1.00.
4
ulServiceMask
4
Number:
0x00000001
Service provider identifier; 1 for compatbility with NT serial.sys.
8
reserved
4
0
12
ulMaxTxQueue
4
Number
Maximum transmit queue size.
16
ulMaxRxQueue
4
Number
Maximum receive queue size.
20
ulMaBaud
4
Number
Maximum baud rate.
24
ulProvSubType
4
Code:
0
1
6
Description
Size of structure in bytes. This must
reflect the total available size, even if
the host requests fewer bytes.
reserved
Indicates kind of device:
Unspecified
RS-232
Modem or TA
All other values are reserved.
28
ulProvCapabilities
4
BitMask
Capabilities Mask. Bits are:
0: DTR/DSR support
1: RTS/CTS support
2: DCD support
3: Can check parity
4: XON/XOFF support
5: Can set XON/XOFF characters
6: reserved
7: reserved
8: Can set special characters
9: Supports 16-bit mode (always 0)
All other bits are reserved.
18
Rev. 0.1
AN571
Table 7. Communication Properties Response (Continued)
Offset
Field
Size
Value
32
ulSettableParams
4
BitMask
Description
Settable parameters mask. Bits are:
0: Can set parity type
1: Can set baud
2: Can set number of data bits
3: Can set stop-bits
4: Can set handshaking
5: Can set parity checking
6: Can set carrier-detect checking
All other bits are reserved.
36
ulSettableBaud
4
BitMask
Settable baud rates mask. Bits are:
0: 75 baud
1: 110 baud
2: 134.5 baud
3: 150 baud
4: 300 baud
5: 600 baud
6: 1200 baud
7: 1800 baud
8: 2400 baud
9: 4800 baud
10: 7200 baud
11: 9600 baud
12: 14,400 baud
13: 19,200 baud
14: 38,400 baud
15: 56,000 baud
16: 128,000 baud
17: 115,200 baud
18: 57,600 baud
19-27: reserved
28: the CP210x supports additional
baud rates other than those defined by
bits 0-18. (There is no way to determine
what these baud rates are, other than by
trying to select them.)
29-31: reserved
Rev. 0.1
19
AN571
Table 7. Communication Properties Response (Continued)
Offset
Field
Size
Value
40
wSettableData
2
BitMask
Description
Capabilities mask for permissible data
bit settings:
0: 5 data bits
1: 6 data bits
2: 7 data bits
3: 8 data bits
4: 16 data bits
5: 16 data bits, extended
6-15: reserved
20
44
ulCurrentTx-Queue
4
Number
Current size of the transmit queue (allocated).
48
ulCurrentRx-Queue
4
Number
Current size of the receive queue (allocated).
52
Reserved
4
BitMask
Reserved
56
Reserved
4
BitMask
Reserved
60
uniProvName
15
“SILABS USB Vx.y” Unicode string identifying the vendor of
the device. The last three characters
indicate the version.
Rev. 0.1
AN571
Table 8. Serial Status Response
Offset
Field
Size
Value
0
ulErrors
4
BitMask
Description
Defines the current error status:
bit 0: break
bit 1: framing error
bit 2: hardware overrun
bit 3: queue overrun
bit 4: parity error
bits 5-31: reserved.
4
ulHoldReasons
4
BitMask
Reason(s) CP210x is holding:
Transmit:
bit 0: waiting for CTS
bit 1:waiting for DSR
bit 2: waiting for DCD
bit 3: waiting for XON
bit 4: XOFF sent, waiting
bit 5: waiting on BREAK
Receive:
bit 6: waiting for DSR
bits 7-31: reserved.
8
ulAmountInInQueue
4
Number
Number of bytes waiting in the input
queue.
12
ulAmountInOutQueue
4
Number
Number of bytes waiting in hte output
queue.
16
bEofReceived
1
Boolean
Always zero.
17
bWaitForImmediate
1
Boolean
0x01 if waiting for an immediate transmission to be sent.
18
bReserved
1
Zero
Reserved for future use.
Table 9. Flow Control State Setting/Response
Offset
Field
Size
Value
Description
0
ulControlHandshake
4
Code
Control handshake: see Table 10 for more
information.
4
ulFlowReplace
4
Code
Control handshake: see Table 11 for more
information.
8
ulXonLimit
4
Number
Threshold for sending XON. When the
available space rises above this amount,
XON will be sent (if in auto-receive mode).
12
ulXoffLimit
4
Number
Threshold for sending XOFF. When available space drops below this amount, XOFF
will be sent (if in auto receive mode).
Rev. 0.1
21
AN571
Table 10. Bits in ulControlHandshake
22
Bit
Name
Size
Value
Description
0-1
SERIAL_DTR_MASK
2
Code
This field controls the state of the DTR output for this interface. The following binary
values are defined:
00: DTR is held inactive.
01: DTR is held active.
10: DTR is controlled by the CP210x
device.
11: Reserved
2
Reserved
1
Flag
Reserved—must always be zero.
3
SERIAL_CTS_HANDSHAKE
1
Flag
Controls how the CP210x interprets CTS
from the end device:
0: CTS is simply a status input.
1: CTS is a handshake line.
4
SERIAL_DSR_HANDSHAKE
1
Flag
Controls how the CP210x interprets DSR:
0: DSR is simply a status input.
1: DSR is a handshake line.
5
SERIAL_DCD_HANDSHAKE
1
Flag
Controls how the CP210x interprets DCD
from the end device:
0: DCD is simply a status input.
1: DCD is a handshake line.
6
SERIAL_DSR_SENSITIVITY
1
Flag
Controls whether DSR controls input data
reception:
0: DSR is simply a status input.
1: DSR low discards data
7-31
Reserved
25
Reserved
Rev. 0.1
AN571
Table 11. Bits in ulFlowReplace
Bit
Name
Size
Value
Description
0
SERIAL_AUTO_TRANSMIT
1
Flag
Controls whether the CP210x acts on
XON/XOFF characters received from the
end device.
0: No XON/XOFF processing.
1: XON/XOFF start/stop output to serial
port.
1
SERIAL_AUTO_RECEIVE
1
Flag
Controls whether the CP210x will try to
transmit XON/XOFF in order to start/stop
the reception of data from an endl device.
If set, XOFF (as defined by the
SET_CHARS command) will be sent by
the CP210x to the end device when the
CP210x’s buffers are more than 80% full
(or as selected by the XOFF threshold).
XON will be sent when the interface’s buffers drop below the XON threshold, as
long as it is fine to do so.
2
SERIAL_ERROR_CHAR
1
Flag
Controls how CP210x handles characters
that are received with errors:
0: The character is discarded.
1: The character is discarded, and the
ERROR special-character is inserted.
The ERROR character must be programmed by the host using the
SET_CHARS messages (Section 5.22).
3
SERIAL_NULL_STRIPPING
1
Flag
If set, any NULL characters received by
the CP210x from the end device will be
discarded and will not be passed to the
host. If clear, NULL characters are treated
as data.
4
SERIAL_BREAK_CHAR
1
Flag
If set, a received break condition causes
the CP210x to insert a BREAK special
character (section 5.18) in the receive
data stream. If clear, BREAK does not
affect the input data stream. In either case,
a received break always causes the
appropriate bit of the error mask to be set.
5
Reserved
1
6–7
SERIAL_RTS_MASK
2
Reserved Reserved
Code
Rev. 0.1
This field controls the RTS line.
00: RTS is statically inactive.
01: RTS is statically active.
10: RTS is used for receive flow control.
11: RTS is transmit active signal.
23
AN571
Table 11. Bits in ulFlowReplace (Continued)
Bit
Name
Size
Value
Description
8–30
Reserved
23
zero
Reserved—must be written as zero.
31
SERIAL_XOFF_CONTINUE
1
Flag
If set, then the CP210x will send XON/
XOFF receive flow control characters to
the end device, even if the end device has
sent XOFF to suspend output and has not
yet sent XON to resume.
Table 12. Special Characters Response
24
Offset
Field
Size
Value
0
bEofChar
1
Number
The character that indicates EOF
(on the input).
1
bErrorChar
1
Number
The character that should be inserted in
the input stream when an error occurs.
2
bBreakChar
1
Number
The character that should be inserted in
the input stream when a break is
detected.
3
bEventChar
1
Number
The special character that causes bit 2
of the event-occurred mask to be set
whenever it is received.
4
bXonChar
1
Number
The character used for XON.
5
bXoffChar
1
Number
The character used for XOFF.
Rev. 0.1
Description
AN571
NOTES:
Rev. 0.1
25
AN571
CONTACT INFORMATION
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26
Rev. 0.1
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