Serial interface

3-wire serial interface

The data serial interface is an RS-232 interface over which RockBLOCK Plus and your host controller transfer commands, responses, and SBD message data. With respect to this interface, RockBLOCK behaves as a DCE (Data Communication Equipment), and the FA behaves as a DTE (Data Terminal Equipment).


TX/RX labelling

  • TXD is an INPUT TO the RockBLOCK
  • RXD is an OUTPUT FROM the RockBLOCK

RockBLOCK 9602/9603 operate the same interface at 3.3V digital signal levels (LVTTL), and are 5V tolerant. If RS-232 voltage levels are needed, the host must include an LVTTL/RS-232 level-shifter.


Arduino Mega 2560

The Arduino Mega works with 5v level (TTL). The RockBLOCK is 5V tolerant and so no level-shifter is required.

RockBLOCK Plus Serial interface voltage levels

Tx Low Maximum-0.5V
Tx High Minimum0.5V
Rx Input Low Threshold-0.5V
Rx Input High Threshold0.5V
Absolute maximum32.0V

RockBLOCK 9602/9603 Serial interface voltage levels

Tx Low Maximum0.6V
Tx High Minimum3.0V
Rx Input Low Threshold0.6V
Rx Input High Threshold3.0V
Absolute maximum5.0V

The RockBLOCK 9602/9603 is 5v tolerant LVTTL, so as such the logic threshold is more like 2.4v as normal.

VOH2.4vapprox 3.3v
VOLapprox 0v0.4v

Baud Rate

Host controllers connecting to RockBLOCK should be configured to the baud rate settings in the table below. Auto baud is not supported.

Baud Rate19200
Data Bits8
Stop Bits1

The baud rate can be set via the AT+IPR command. You are advised not to change the baud rate so the RockBLOCK uses a reliable, fixed baud rate.

Flow control


It is strongly recommended to use RockBLOCK with flow control disabled.

The flow control setting can be set by AT commands. RockBLOCK has flow control disabled during manufacture, but should the device be reset to defaults then the following commands will disable flow control:

/* Issue AT command */


/* Receive response */


/* Disable Flow Control */


/* Receive response */


/* Save configuration in non-volatile memory */


/* Receive respone */


AT commands in this chapter