A shared repository to provide a description of reverse-engineered glucometer protocols

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Abbott Shared HID protocol

Multiple Abbott devices of the FreeStyle family share a common communication protocol based on USB HID. These devices all provide a direct USB connector and require no special cable nor driver to speak with a PC.

While most of the commands are not compatible between each other, the devices do share a basic framing protocol and basic text command format.

Credit for the reverse engineering go to Xavier Claessens for OpenGlucose.

Communication Protocol

These devices appears on the USB bus as a HID device. The communication between the software and the device happens through HID Set Report/Get Report interfaces, in a way that is compatible with the Linux hidraw interface.

In particular the packets are sent on the Control endpoint, as Class Interface messages (bRequestType = 0x21, bRequest = 0x09, wValue = 0x0200, wIndex = 0x0000), and received on the interrupt endpoint (0x81). Report numbers are not used.

The “reports” are not following the HID standard. They are of a fixed 64-bytes size, even if most of the commands themselves are shorter. Replies can span multiple inbound reports.

message = message-type message-length 62OCTET
message-type = OCTET  ; this will more properly defined later.
message-length = %x00-3E

The message-type is not fully understood, and its values differ between different devices, and are thus not part of this document.

The message-length represent the number of significant bytes in the message excluding type and length.

Initialization Sequence

The devices following this protocol share the same initialization sequence, sending four messages with no payload. The content of the replies could be used to validate whether the device is the one expected, but their meaning is not fully understood.

init-command = %x04 %x00
init-command-reply = %x34 %x01 OCTET

The octet returned by this command appears not to be constant per device, according to Xavier’s notes and experimentation. It is not constant across devices. No meaning is known for this.

init-query-serial = %x05 %x00
init-query-serial-reply = %x06 %x0e
                          ( serial-number / no-serial-number ) %x00
serial-number = 7( ALPHA / DIGIT ) "-" 5( ALPHA / DIGIT )
no-serial-number = "00000000 (No SerialNum)"

Note: the serial number definition is common to most Abbott device, except newer devices have a longer, and non-compatible serial number format. It is possible that the Abbott software can determine the driver to use based on this serial number.

init-query-swver = %x15 %x00
init-query-swver-reply = %x35 message-length software-version %x00
software-version = VCHAR *( VCHAR / SP )

The software version definition is effectively free-form. Newer models appear to include a date.

init-complete = %x01 %x00
init-complete-reply = %x71 %x01 %x01

This is the same exact request/reply pair in all the currently observed devices.

Synchronization packets

Some devices send what appears like a “synchronization packet” every few reports read, that is so defined:

synchronization-packet = %x22 %x01 OCTET

The frequency of these packets appears to depend on the device (some devices appear to send it exactly every three reports sent), and so does the content of the packet.

Text commands

Most of the devices using this HID-based protocol can be sent commands that receive ASCII text responses. These responses can span multiple frames, allowing the single response to cross the 62-bytes length limit.

Each text response, once reconstructed, complies to the following specs:

response = message "CKSM:" checksum CRLF
           "CMD" SP command-status CRLF

checksum = 8HEXDIG
message = *( VCHAR / SP / CRLF )
command-status ("OK" / "Fail!")

The <checksum> is calculated by summing up the ASCII value of each of the bytes forming the message, including the final newline that usually terminates the message.

Since no message is present in case of message failure, the checksum is null and is represented by the string 00000000.

Multiple records commands

Different commands can return a list of records. While their meaning depends on the issued command, the reported format fits the same syntax:

multi-records = *( record CRLF )
                record-count "," checksum

record = *( value "," ) value
value = *VCHAR
record-count = 1*DIGIT
checksum = 8HEXDIGIT

The <record-count> field will contain the number of records that were returned; the <checksum> field is calculated the same way as the overall command one by summing up the ASCII value of each of the bytes forming the record set, up to and including the final newline, and excluding the record count.

Common commands

There are a number of commands that appear shared across FreeStyle devices, and are thus documented here to avoid duplication.

As devices may not support all these common commands, please refer to the detailed protocol definition to note inconsistencies.

The majority of these commands are getters and setters of variables, some free-form and some structured. The generic syntax for these commands is:

command = "$" variable-name ( "?" / "," variable-value )
variable-name = 1*VCHAR
variable-value = *( VCHAR / SP )

Some variable (such as the software version and serial number) are read-only. Those commands are documented with their full value, including the terminating question mark.


swver-response = 1* ( VCHAR / SP ) CRLF

Returns the software version of the device. The returned value is free-form, as it changes among devices.


serlnum-response = 1* ( ALPHA / DIGIT ) CRLF

Returns the serial number of the device. The serial number format appears to be different from previous Abbott devices and as such is to be considered free-form.

Please note that this command may provide a serial number even for devices that respond with <no-serial-num> during initialization.


date-cmd = "$date" ("?" / "," date-value)
date-query-response = date-value CRLF

date-value = ( month "," day "," year )
month = 1*2DIGIT
day = 1*2DIGIT
year 1*2DIGIT

Fetch or set the current date as seen by the device. If a date value is passed following the command, it’ll be interpreted as a set-date.

Note the year value is defined at most with two digits, the value 2000 needs to be added (or subtracted) to match the current year.

In case of successful setting of date, the command is confirmed with no further information; in case of error, the <message> field will report the encountered error.


time-cmd = "$time" ("?" / "," time-value)
time-query-response = time-value CRLF

time-value = hour "," minute
hour = 1*2DIGIT
minute = 1*2DIGIT

Fetch or set the current time as seen by the device.

In case of successful setting of date, the command is confirmed with no further information; in case of error, the <message> field will report the encountered error.


ptname-cmd = "$ptname" ("?" / "," patient-name)
ptname-query-response = patient-name CRLF

patient-name-setting = 1*VCHAR
patient-name-response = *VCHAR

Returns the patient name as configured in the device.

Note that while an empty response is valid, an empty value when setting the variable is not accepted.


ptid-cmd = "$ptname" ("?" / "," patient-id)
ptid-query-response = patient-id CRLF

patient-id-setting = 1*VCHAR
patient-id-response = *VCHAR

Returns the patient ID as configured in the device.

Note that while an empty response is valid, an empty value when setting the variable is not accepted.