Data Acquisition Interface Protocol

Packet Structure

Serial messages have a packet structure consisting of a string of bytes with the following form:

• The synchronization character is transmitted during idle periods in response to any received character, to enable the link to be synchronized in baud rate. Details are given in the full specification document.

• The address is a 5 bit representation of the module identifier used to address a specific module in a multiple-module environment.

• Packet type is a 3 bit word that allows different packet structures to be used, for example, very short cut-down packets for real-time commands, broadcast commands etc. The use of different packet types will be minimized in order to manage the complexity of the interface. Some AVR microcontrollers have as much as 128KBytes of Flash memory, and may be able to handle such complexity.

• The data length includes the command and all parameters and data following, but excludes the checksum and end-of-message character.

• The number of data bytes present can be from 0 to a limit that is dependent on the internal buffer size in the DAU. This is nominally 16.
  

Commands are defined below. There is scope for a very large number of these but in practice we aim to develop rather generic commands and minimize specialized commands so that the interface is kept simple. It must be independent of the microcontroller used.

Commands

• Unit ID Read (0x1). This command causes the microcontroller to return a small amount of information about its capabilities and athe address of the unit information block.

• Read Memory (0x2). This causes a block of internal EEPROM memory to be passed back to the PC.

• Write Memory (0x3). This causes a block of internal EEPROM memory to be written to the device, overwriting the contents.

• Read I²C Memory (0x4). This causes a block of external EEPROM memory to be passed back to the PC.

• Write I²C Memory (0x5). This causes a block of external EEPROM memory to be written to the device, overwriting the contents.

• Read and Reset Data Memory Buffer (0x6). This command allows the captured data to be downloaded to a PC and the buffer to be reset ready for more captures.

• Reset Real Time Clock (0x7). The real time clock is reset to zero.

• Error (from microcontroller) (0x10). This returns an error code and any additional qualifying information defined for the error.

• Success (from microcontroller) (0x11). This returns requested data if any.

• Offset Calibrate (0x20). This command causes the microcontroller to run an offset calibration on the DAU. In the case that the DAU has an analogue input module, this shall short the inputs and an A/D converter read shall be executed on the specified channel and programmable gain setting.

• Single Read ADC Command (0x21). Start and read the A/D converter immediately on the specified channel and programmable gain setting.

• Multiple Read ADC Command (0x22). Create a process to start and read the A/D converter at specified intervals until the data memory buffer is full. Once started, this command will return an error if another command is received while the process is still active.
  

• Set ADC Conversion Information (0x23). This writes a channel control byte to control the parameters of the ADC conversion process.

• Abort ADC Process (0x24). This aborts the ADC conversion process.

• Firmware Upload (0x40). This causes the program to jump to a bootloader. If no bootloader is present, this simply resets the microcontroller.
  

• Debug Read SRAM (0x42). This causes a block of internal SRAM memory to be passed back to the PC.

• Debug Write Memory (0x43). This causes a block of internal SRAM memory to be written to the device, overwriting the contents.

• Debug Set Port Bit (0x44). This causes a specified bit of a particular I/O port to be set.

• Debug Clear Port Bit (0x45). This causes a specified bit of a particular I/O port to be cleared.

• Debug Read Port Input Pins (0x45). This causes the I/O pins of the specified I/O port to be read. The AVR devices have a separate register for each external I/O port, for the values that were written to the port for the output pins, and another address to read the external signals presented at the pins that are set as inputs. This command accesses the latter.