TaiDoc TD-42xx

Reverse engineered by Diego Elio Pettenò. With thanks to Gianni Ceccarelli for the time fields structure.

The protocol is compatible with both TD-4277 and TD-4235B devices at least.

These devices are marketed as:

  • GlucoRx Nexus
  • GlucoRx NexusQ
  • Menarini GlucoMen Nexus
  • Aktivmed GlucoCheck XL

Important device notes

The device has a miniUSB-A connector and comes with an onboard HID-to-Serial adapter, based on the Silicon Labs cp2110 interface.


Device Vendor ID Product ID
GlucoRx Nexus 10c4 ea80
GlucoRx NexusQ 10c4 ea80

Serial port configuration

The CP2110 bridge should be configured as follows:

  • 8 data bits;
  • no parity bits;
  • 1 stop bit;
  • 19200 baud rate.

Supported Features

The meter hardware supports:

  • Factory-fixed mg/dL or mmol/L user reported unit. Values are always returned by the protocol in mg/dL.
  • Meal flags (none, pre-meal, post-meal).
  • Sound and reminder alarms.


Packet Structure

The device uses a simple challenge and response serial protocol with fixed-size 8-bytes commands and responses.

packet = STX command-id message direction checksum
STX = %x51

command-id = OCTET
message = 4OCTET
empty-message = %x00 %x00 %x00 %x00

direction = direction-in / direction-out
direction-in = %xA5
direction-out = %xA3

checksum = OCTET

The checksum is calculated as a full sum of the first seven bytes of the packet, and then truncated to 8-bit.


Connection is established by sending a connection command, and receiving a response.

message-connect = %x00
command-connect = %x22
response-connect = %x22 / %x24 / %x54

In both the request and long response packets, the message is zero.

Get Model

To confirm the model of the device (probably to avoid confusing with other devices sharing a similar protocol), you can send command 0x24.

model-request = STX %x24 empty-message direction-out checksum
model-response = STX %x24 model OCTET OCTET direction-in checksum

model = OCTET %x42  ; 16-bit little-endian value

The model will be reported as a 16-bit little-endian BCD value.

Date and Time


All representation of time for this protocol are idential, and they follow this format:

datetime = day minute hour
day = 2OCTET  ; 16-bit little endian value.
minute = OCTET
hour = OCTET

While minutes and hours are left unpacked, the day field packs the full year, month and day into a single 16-bit integer.

Within the 16-bit day field, the first 7 bits represent the year, starting with 2000, followed by 4 bits for the month (range 1-12), and 5 bits for the day (range 1-31).

Getting Time

To retrieve the time of the device, you send the command 0x23 with a zero message, and parse the returned message as the date and time.

gettime-request = STX %x23 empty-message direction-out checksum
gettime-response = STX %x23 datetime direction-in checksum

Setting Time

To set the time of the device, you send the command 0x33 with the time as message.

settime-request = STX %x33 datetime direction-out checksum
gettime-response = STX %x33 datetime direction-in checksum

Reading Records

To retrieve the records from the device, you need to first request the number of records, and then retrieve the timestamp and the value and flags for each record.

Record count and record index are 16-bit unsigned integers, little-endian, and are 0-indexed, with the most recent result first.

record-id = 2OCTET  ; 16-bit little-endian value

Record Count

To retrieve the record count, send command 0x2B.

recordcount-request = STX %x2B empty-message direction-out checksum
recordcount-response STX %x2B record-count unknown-value direction-in checksum

record-count = 2OCTET  ; 16-bit little-endian value
unknown-value = 2OCTET  ; likely 16-bit little-endian value

The unknown-value is unknown but appears to be bound to the record-count. For a new meter with a record count of 0 (or a cleared meter), the unknown value is always 0xFFFF.

Record Timestamp

To retrieve each record timestamp, send command 0x25.

record-timestamp-request = STX %x25
                           record-id %x00 %x00 direction-out checksum
record-timestamp-response = STX %x25 datetime direction-in checksum

Record Value

To retrieve each record value, send command 0x26.

record-value-request = STX %x26 record-id %x00 %x00 direction-out checksum
record-value-response = STX %x26
                        glucose-value unknown meal-flag direction-in checksum

glucose-value = 2OCTET  ; 16-bit little-endian value
unknown = OCTET
meal-flag = meal-none / meal-before / meal-after
meal-none = %x00
meal-before = %x40
meal-after = %x80

Clearing Memory

To completely clear the memory of the device, send command 0x52.

clear-memory = STX %x52 empty-message direction-out checksum