Serial Interface
All RockBLOCK products communicate with a host controller using a simple 3-wire asynchronous serial connection (TX, RX, and GND).
The signalling standard differs depending on the model:
- RockBLOCK Plus uses a true RS-232 interface.
- RockBLOCK 9602/9603 use LVTTL UART logic levels (3.3 V, 5 V tolerant).
The sections below describe each variant in detail, followed by information that is shared across all models.
RockBLOCK PLUS Serial Interface
The data serial interface is an RS-232 interface through which RockBLOCK Plus and your host controller transfer commands, responses, and SBD (Short Burst Data) message data. Within this setup, RockBLOCK functions as DCE (Data Communication Equipment), and the FA (Field Application) acts as DTE (Data Terminal Equipment).
RockBLOCK Plus Serial interface voltage levels
| Parameter | Value |
|---|---|
| Tx Low Maximum | -0.5V |
| Tx High Minimum | 0.5V |
| Rx Input Low Threshold | -0.5V |
| Rx Input High Threshold | 0.5V |
| Absolute maximum | 32.0V |
RockBLOCK 9602 & 9603 Serial Interface
RockBLOCK 9602/9603 Serial Interface Voltage Levels
The RockBLOCK 9602/9603 uses 3.3 V logic (LVTTL) on its UART pins, but it is tolerant of 5 V signals. This means:
- When RockBLOCK drives its TX pin (output), voltages will be close to 0 V (logic LOW) or ~3.3 V (logic HIGH).
- When your host drives the RX pin (input), RockBLOCK will reliably detect LOW if the voltage is under 0.8 V, and HIGH if above 2.0 V.
- The RX pin can safely tolerate up to 5.5 V without damage.
| Parameter | Min | Max | Notes |
|---|---|---|---|
| VOH (Output HIGH) | 2.4 V | ~3.3 V | RockBLOCK TX driving logic HIGH |
| VOL (Output LOW) | 0 V | 0.4 V | RockBLOCK TX driving logic LOW |
| VIH (Input HIGH threshold) | 2.0 V | 5.5 V | Host TX must drive at least 2.0 V for RockBLOCK to read HIGH |
| VIL (Input LOW threshold) | –0.3 V | 0.8 V | Host TX must drive below 0.8 V for RockBLOCK to read LOW |
| Absolute Maximum Input | – | 5.5 V | Never exceed this on RX pin |
In RockBLOCK validation testing, the following stricter thresholds were confirmed:
- TX High Minimum: 3.0 V
- TX Low Maximum: 0.6 V
- RX Input High Threshold: 3.0 V
- RX Input Low Threshold: 0.6 V
These reflect the guaranteed design margins, which are slightly tighter than standard LVTTL specs.
Shared Serial Interface Information
- TXD is an INPUT to the RockBLOCK.
- RXD is an OUTPUT from the RockBLOCK.
- GND must always be connected — it serves as the common electrical return path and a reference point for the TX and RX signals, stabilising the data transfer by reducing noise and ensuring signal integrity.
The Arduino Mega works with 5v level (TTL). The RockBLOCK is 5V tolerant and so no level-shifter is required.
Baud Rate
Host controllers connecting to RockBLOCK should be configured to the baud rate settings in the table below.
| Setting | Value |
|---|---|
| Baud Rate | 19200 |
| Data Bits | 8 |
| Parity | None (N) |
| Stop Bits | 1 |
You are advised not to change the baud rate so the RockBLOCK uses a reliable, fixed baud rate. Automatic baud rate adjustment settings are not supported.
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 */
AT\r
/* Receive response */
OK\r
/* Disable Flow Control */
AT&K0\r
/* Receive response */
OK\r
/* Save configuration in non-volatile memory */
AT&W0\r
/* Receive response */
OK\r