R7 Serial: Send Data

Payload Size

The maximum packet size for an SBD MO is 340 bytes.
The maximum user-definable payload size is 336 bytes (WH, WHNC) or 321 bytes when also requesting GPS data (WHP, WHNCP)

Checksum Required for Some Commands

When sending data using commands like WH or WHP, you must prepend a CRC-CCITT (XModem) checksum to the hex payload.

This checksum helps the receiving system detect accidental errors in transmission.

• Example input: ASCII string "123456789"
• Expected checksum: 0x31C3 (in hex: 31c3)
• You would send: R7+WH=31c3<your-hex-data>\r

Need to compute it? You can use a Python snippet or an online tool that supports CRC-CCITT (XModem).

Transmit Hex Encoded Data

Serial Command	Function
R7+WH=	Sends user defined hexadecimal data. Hexadecimal data must be preceded by checksum.
R7+WHP=	Sends user defined hexadecimal data and GPS position data. Hexadecimal data must be preceded by checksum.
R7+WHNC=	Sends user defined hexadecimal data. No Checksum used.
R7+WHNCP=	Sends user defined hexadecimal data and GPS position data. No Checksum used.

Send Hex Data with Checksum

R7+WH=<checksum><hex payload>

This command instructs the device to send user-supplied data. The device will respond with a message ID, which can be used later to query status.

/* Transmit "Hello World" (Hex: 48656c6c6f20576f726c64, Checksum: 992a)

R7+WH=992a48656c6c6f20576f726c64\r

/* Receive Response */

<Outbound MessageID>\r
OK\r

Send Hex + GPS with Checksum

R7+WHP=<checksum><hex payload>

This command instructs the device to send user-supplied data and GPS position data. The device will respond with a message ID, which can be used later to query status.

/* Transmit "Hello World" (Hex: 48656c6c6f20576f726c64, Checksum: 992a)

R7+WHP=992a48656c6c6f20576f726c64\r

/* Receive Response */

<Outbound MessageID>\r
OK\r

Send Hex Data (No Checksum)

R7+WHNC=<hex payload>

This command instructs the device to send user-supplied data. The device will respond with a message ID, which can be used later to query status.

/* Transmit "Hello World" (Hex: 48656c6c6f20576f726c64)

R7+WHNC=48656c6c6f20576f726c64\r

/* Receive Response */

<Outbound MessageID>\r
OK\r

Send Hex + GPS (No Checksum)

R7+WHNCP=<hex payload>

This command instructs the device to send user-supplied data and GPS position data. The device will respond with a message ID, which can be used later to query status.

/* Transmit "Hello World" (Hex: 48656c6c6f20576f726c64)

R7+WHNCP=48656c6c6f20576f726c64\r

/* Receive Response */

<Outbound MessageID>\r
OK\r

---

Transmit Binary Encoded Data

Serial Command	Function
R7+WB=	Sends user defined binary data with checksum.
R7+WBP=	Sends user defined binary data with checksum and GPS position data.
R7+WBNC=	Sends user defined binary data.
R7+WBNCP=	Sends user defined binary data and GPS position data.

Send Binary Data with Checksum

R7+WB=<length>

This command instructs the device to send user-supplied data. The device will respond with a message ID, which can be used later to query status.

/* Prepare device to receive binary data */
/* Length = byte size of binary payload */

R7+WB=[length]\r

/* Receive response */

OK\r

/* Device is now listening for binary data */

<binary data>\r

/* Receive response */

<Outbound MessageID>\r
OK\r

Send Binary + GPS with Checksum

R7+WBP=<length>

This command instructs the device to send user-supplied data and GPS position data. The device will respond with a message ID, which can be used later to query status.

/* Prepare device to receive binary data */
/* Length = byte size of binary payload */

R7+WBP=[length]\r

/* Receive response */

OK\r

/* Device is now listening for binary data */

<binary data>\r

/* Receive response */

<Outbound MessageID>\r
OK\r

Send Binary Data (No Checksum)

R7+WBNC=<length>

This command instructs the device to send user-supplied data. The device will respond with a message ID, which can be used later to query status.

/* Prepare device to receive binary data */
/* Length = byte size of binary payload */

R7+WBNC=[length]\r

/* Receive response */

OK\r

/* Device is now listening for binary data */

<binary data>\r

/* Receive response */

<Outbound MessageID>\r
OK\r

Send Binary + GPS (No Checksum)

R7+WBNCP=<length>

This command instructs the device to send user-supplied data. The device will respond with a message ID, which can be used later to query status.

/* Prepare device to receive binary data */
/* Length = byte size of binary payload */

R7+WBNCP=[length]\r

/* Receive response */

OK\r

/* Device is now listening for binary data */

<binary data>\r

/* Receive response */

<Outbound message ID>\r
OK\r

---

Additional Commands

Assign a Custom Outbound Message ID

R7+[WH|WHNC|WHP|WHNCP|WB|WBNC|WBP|WBNCP],ID=n

Allows you to set a custom Outbound Message ID, used in combination with send hex or binary data commands.

This ID is not transmitted over the Iridium network — it is stored locally and used only for device-side tracking and status queries.

/* Transmit "Hello World" (Hex: 48656c6c6f20576f726c64)*/
/* Set the Outbound Message ID to '1234' */

R7+WHNCP=48656c6c6f20576f726c64,ID=1234\r

/* Receive response */

1234\r
OK\r

/* Prepare device to receive binary data */
/* Length = byte size of binary payload */

R7+WB=[length],ID=1234\r

/* Receive response */

1234\r
OK\r

/* Device is now listening for binary data */

<binary data>\r

/* Receive response */

1234\r
OK\r

Check Outbound Message Status

R7+STAT=n

This command requests the transmission status of a specific outbound message. The device will respond with a status number.

/* Check message status */

R7+STAT=<Outbound Message ID>\r

/* Receive response */

<Status #>\r
OK\r

Response	Meaning
0	Message not sent
1	Message sent

---

Error Messages

Error Type	Description
ERROR 0	Data format error - eg. - Non-hex payload - Incorrect checksum provided - Binary payload timeout
ERROR 1	Device deactivated - will not be seen as device is unable to respond in deactivated state
ERROR 2	This error type will be returned in response to any R7+WH.. or R7+WB.. message commands if the database is full.
ERROR 3	This error will be returned to indicate rejection of a message command when the submitted ID is a duplicate of one already in the DB and not yet sent.